Teledyne Hastings Instruments Blog

Teledyne Hastings’ Mass Flow Controllers (MFC) are used in a very wide range of applications in numerous markets. In this blog, we are going to briefly explore the use of Teledyne MFCs to improve the surface properties of certain metals such as steel. Nitriding, in which a nitride layer is added, can also be used on aluminum and titanium.

There are three methods of nitriding: gas nitriding, salt bath nitriding, and plasma nitriding. (“Nitriding”, Wikimedia Foundation, 1/18/2023, https://en.wikipedia.org/wiki/Nitriding ). We are going to focus solely on gas nitriding. In this process, ammonia gas flow can be controlled into a furnace at several hundred degrees Celsius. The furnace is hot, but not so hot as to risk damaging or structurally modifying the part. Now the incoming gas can be controlled using a high-capacity mass flow controller. After the gas is admitted, the ammonia molecules (NH₃) from the gas dissociates into nitrogen and hydrogen at the surface of the part being treated. The monatomic nitrogen can then diffuse into the surface of the part and form a nitride coating layer.

What are some of the benefits of nitriding? First, the treated part will generally have an increased hardness which in turn will give the part improved wear resistance. Also, many parts that have been treated with the nitride process will be less susceptible to corrosion.

There are many types of parts that are given nitride treatment.

• Gears and splines
• Shafts and bearings
• Valve components
• Extrusion dies
• Rollers for continuous crimping

In large furnaces, high flows of ammonia gas are required, and Teledyne is able to supply mass flow controllers that are accurate, stable, and fast. We are ready to help. Contact us and we will help you size a flow controller for your nitride application.

In addition to our analog 200 Series mass flow controllers, we can also provide our Digital 300 Series (“A” and “B” Models) which feature excellent accuracy ± (0.2% full scale + 0.5% of reading) , fast response, and flexibility. “A” models can be built with IP-67 enclosure which offers protection against external dust and liquids. “B” models can be configured with an optional color touchscreen display. Both “A” and “B” models provide digital and analog (0-5 VDC, 0-10 VDC, 0-20 mA, 4-20 mA) input and output. Both have internal totalizer feature so the user can track the total amount of ammonia gas used in a nitride heat treat cycle. Free user software is provided (but is not required) and, for LabVIEW^™ users, free certified drivers are available from ni.com.

If you have a nitride process or any other application that requires precision gas control, we would very much like to hear from you. You can contact us by phone (757-723-6531), email (hastings_instruments@teledyne.com) or via LiveChat at www.teledyne-hi.com  

We are starting a new blog series where we will introduce you to some of the key employees here at Teledyne Hastings. Our first blog in this series will focus on our domestic sales manager, Will Harrison.

In addition to being domestic sales manager, Will works as a sales application engineer ensuring that customers select the best flow or vacuum product for their application/system. Will also works with our USA channel partners and keeps them informed of the latest products and markets for Teledyne Hastings’ products and services. Will has been with Teledyne for over thirty-five years.

 Let’s ask Will some questions to get to know him better.

• How did you start working at Teledyne Hastings? 
  I had a close friend that worked here who mentioned the expanding sales team was looking to hire a new sales application engineer. It seemed to happen very fast … I applied, was interviewed, and was hired in less than two weeks.

• What is a typical day like for you?
  I am always available for customer phone calls. I enjoy hearing about new opportunities or helping customers improve an existing vacuum or flow application. When not on the phone, you might find me generating a quote for a customer or helping out one of our USA sales channel partners. I also travel with our distributors as we look for new opportunities for Teledyne Hastings.

• Let’s follow up on that, where is one of your favorite places where you have for traveled for work?
  The best place I ever traveled was Vancouver BC. Vancouver is a neat place to venture out, see the sites, and enjoy great food. Our distributor drove us up to see Whistler, which was awesome! At the time, that area had a few startup companies focused on the fuel cell industry and our mass flow meters and controllers were enjoying great success.

• Outside of work, what is it that you like to do?
  I like to run and bike when time permits. I like to do half marathons and full marathons. I’ve even completed a full “ironman” triathlon. I also enjoy Old Dominion University (ODU) sports where I got my degree. The Lady Monarchs won back-to-back national titles in women’s basketball (1979, 1980) before the NCAA became involved. The excitement from the crowds at the ODU sporting events is great.
  
  

• What is one part of the job that you find rewarding? 
  I enjoy working with our sales channel partners and customers to provide solutions for a wide variety of applications. I also enjoy working with my colleagues on the sales team and other members of the Teledyne Hastings Team.

In this series, we hope that every reader will be able to learn a little more about the employees they interact with here at Teledyne Hastings. If you call for support or sales, we all have a story and we would like to share that story with you.  Visit  https://info.teledyne-hi.com/blog to read more about our vacuum gauges and mass flow meters and mass flow controllers. (And look for future postings about Teledyne Hastings’ employees.)

Will Harrison (right) after finishing the 2022 Honolulu Marathon. Brother Glen is on the left.

To learn more about Teledyne Hastings and the products we make, visit our website or click below. 

Teledyne Hastings has a broad offering of thermal mass flow meters, mass flow controllers, and vacuum instruments. Within each of our digital product families, we offer both analog output (e.g. 0-5 VDC, 0-10 VDC, and 4-20 mA) and digital outputs (RS232, RS485, and USB). Typically, our customers will interface our instruments to their data acquisition systems. But, in some cases, our users want a fast and easy method to configure, control, and collect data with our instruments. In this blog, we will discuss our Windows-based programs. Specifically, we will answer three questions:

1. What do our Windows-based interface programs do?
2. How do you use the Windows software?
3. Where can I download the Teledyne Hastings free Windows user software?

Before we start, we want to tell you that all of our instrument software, including DisplayX for the THCD-101 and THCD-401 power supplies, is FREE. We don’t charge for these routines so there is a limit to how much technical support we provide for software. But, if you run into an issue, we will try to help. Typically, software issues are associated with the PC and not with the flow or vacuum instrument.

1. What do our Windows-based interface programs do?

CONFIGURATION: Our instruments are configured and shipped according to the selections given to us before order entry. Generally, our instruments are “plug and play”. But in some cases, the end-user may decide that they want to change the configuration. For example, it may be the case that a different set of units is more convenient. Or, in the case of a flow instrument, a different gas record needs to be selected. Our Windows-based code makes it very easy to make a selection and write it to the instrument’s memory. Our Digital 300 Series has many features including multiple gas record capability, totalizer, and control valve soft-start. All of these can be modified with our free Windows-based user software.

CONTROL: In some cases, the user may want to get up and running very quickly to test system parameters before they interface to a PLC. Our routines allow easy control and the user has the option to open a window to view live vacuum or flow data as a function of time. And the user can display a graphical window which shows performance over a stretch of time. In the case of a flow controller, the user can enter flow setpoint commands using a numeric input, or slider bar.

Data Logging: Perhaps the most popular use of our Windows-based programs is the ability to set up and record data to an Excel (csv) file with a user-defined interval over a long period of time. This allows the user to perform tests overnight or over several days. There is a limit to the number of data points that can be stored. So the user must take that into consideration when setting up the test.

For starters, you will need to connect a serial cable (RS232, RS485, or USB) from your laptop to either the 300 Vue mass flow instrument or our HVG-2020 vacuum gauge. In this example, I will connect to an HFC-D-302B digital mass flow controller. But, the initial steps are identical for the HVG-2020 Series vacuum gauges. A USB cable (micro-B) is very convenient to use because these cables can usually be found at “dollar” stores. (And yes, they only cost about a dollar.) The USB connector serves as a virtual COM port for serial communication, eliminating the need for a USB to Serial converter.

Once connected, you simply run the Windows executable program and the following window will popup:

At this point, you need to serially connect to the instrument. You do this by clicking on Operation

and then clicking on Connect

Now, in the case shown here, my cable is connected to COM Port #4 and when I select COM4 in the drop-down menu, the window shows the digital setpoint (in blue) and the actual flow rate (in red).

Once the unit is connected, there are several additional windows that can be opened. You can click on VIEW and see the choices.

If you are operating a flow controller, the next window you will likely want to open is SetPoint. This window allows you to control the MFC by typing a setpoint command in the entry field at the top, sliding the selector on the left, or clicking one of the boxes on the right.

The Operation menu has many useful features, especially for configuring the 300 Vue mass flow controller. And, if you want to log data over a long period of time, you will set that up using the Logging menu.

3. Where can I download the Teledyne Hastings free Windows user software?

You can request the software from our website. The link is given here: https://www.teledyne-hi.com/en-us/resource-center/software

Please note that we must comply with US export regulations, so we are required to know the names and addresses of all folks who request our software. Once you have completed the short form and we have reviewed, one of our application engineers will send the requested software to you via a secure file transfer site.

One other note we would like to make about digital communication with our vacuum and flow products. In addition to the Windows software, we also have certified LabVIEW drivers for all of our digital products. And for our flow power supplies (THCD-101 & THCD-401), we provide free software (DisplayX).

300 Vue Mass Flow LabVIEW Driver – Click Here HVG-2020A Vacuum Gauge LabVIEW Driver – Click Here HVG-2020B Vacuum Gauge LabVIEW Driver – Click Here DCVT Vacuum Gauge LabVIEW Driver – Click Here DAVC Vacuum Gauge LabVIEW Driver – Click Here THCD-101 Flow Power Supply LabVIEW Driver – Click Here THCD-401 Flow Power Supply LabVIEW Driver – Click Here

And as always, we are here to help. If you have any questions about any of our vacuum or flow products, you can reach out to us by phone (800-950-2468/757-723-6531), email (hastings_instruments@teledyne.com) , or via LiveChat on our website (www.teledyne-hi.com )

Microsoft, Windows, Internet Explorer, Microsoft Edge, OneDrive, and Microsoft Excel are trademarks, or registered trademarks of Microsoft Corporation in the United States and other countries.

In this blog, we will discuss various system connections, or fittings, that are available for both our mass flow and vacuum products. We will briefly explore why you might select a particular family of fittings for your system. Also, we will touch on some basic installation Dos and Don’ts.

Mass Flow Meters and Mass Flow Controllers

Many users of low flow (0-5 sccm up to 0-25 slm) instruments appreciate the convenience of compression fittings. The Swagelok ™ brand of compression fittings is very popular, and many users ask for these by name. Compression fittings can be very reliable; also, they can be quickly uninstalled and reinstalled as needed. And, unlike VCR ™ and VCO ™ fittings (we will talk more about these in a minute), compression fittings do not require a separate o-ring or single-use gasket. Our flow products are offered with various size Swagelok™ brand compression fittings. While the 1/4” size is the most popular for many low flow applications, we also offer, even smaller, 1/8” size as well. Metric sizes, including 10 mm and 12 mm, are also available. Then, for even higher flow applications, we also offer 1/2”, 3/4”, 1”, 1.5” and even 2” Swagelok ™ fittings. Note that the largest compression fittings require a swaging tool. (Link?)

Per the “Tube Fitter’s Manual” published by Swagelok®, here are the steps for manual installation of Swagelok Tube Fittings up to 1 in. or 25 mm.

1. Fully insert the tube into the fitting and against the shoulder; rotate the nut finger tight.
   
   
   
2. Mark the nut at the 6 o’clock position.
   
   
   
   
3. While holding the fitting body steady, tighten the nut 1 ¼ turns to the 9 o’clock position.
   For 1/16, 1/8, and 3/16 in. or 2, 3, and 4 mm tube fittings, tighten the nut ¾ turn to the 3 o’clock position.
   
   

Reassembly Procedure is as follows:

1. Prior to disassembly, mark the tubing at the back of the nut, mark a line along the nut and body flats. Use these marks to ensure that you return the nut to the previously pulled-up position.
   
   
   
2. Insert the tubing or tube adapter end connection with pre-swaged ferrules into the fitting until the front ferrule seats against the fitting body.
   
   
3. While holding the fitting body steady, rotate the nut with a wrench to the previously pulled-up position, as indicated by the marks on the tubing and flats. At this point, you will feel a significant increase in resistance. Tighten the nut slightly.
   
   

The VCR ™ system from Swagelok™ is very popular with users who need high purity, all-metal, reliable sealing for either positive pressure or vacuum applications. For these fittings, a gasket, usually metal, is used to seal between the two symmetric sealing faces. In some cases, an elastomeric or PTFE gasket can be used. Metal gaskets (e.g. copper, nickel, or stainless steel) in VCR ™ connections should only be used once. Metal gaskets can be purchased with a retainer to hold the gasket in place when installing. The gasket is secured between the mating surfaces and the nut is drawn finger tight. Then, to finish installation, two wrenches are used to tighten the connection and create the leak-free seal. Note that copper gaskets require a 1/4 turn (90°) beyond finger tight while nickel and stainless steel only require an 1/8 (45°) of a turn.

HFC-302 with VCR fittings

The VCO™ system is convenient when the user wants to have fast make and break connections. It is also handy when space is limited. One part of the VCO™ connection includes an o-ring while the mating connection has a flat smooth finish. Installation is easy. A nut is made finger tight and then a wrench is used to tighten by 1/8 (45°) of a turn.

Usually, your fitting selection and piping are going to be a function of the flow rate. Our application engineers are available via email, phone or LiveChat to help you.

Vacuum Gauges

There are several popular systems of connections for vacuum gauges. Selection of a system should be driven by base pressure, outgassing load, and of course, cost.

For many users who just need to reach the mTorr range of pressures, tapered pipe thread (NPT: National Pipe Tapered) connections are simple, require no external clamps or bolts, and can be assembled quickly. However, PTFE tape or some other sealant should be used on the threads for two reasons. First, the tape/sealant fills the void between the mating thread surfaces and second, the tape/sealant acts as an anti-galling lubricant between the threads.

When wrapping PTFE tape onto NPT threads, start with clean surfaces and a clean cut of the tape. Make sure the tape is flat as it is wound onto the sealing surfaces and wrap in the direction of the threads. Two to three wraps is adequate. End the wrap with a clean cut of the tape. Tighten the connection with a wrench. How tight? Well, there is no right answer except to say that you want the system to seal, but you don’t want the threads to strip. So, use a wrench until tight, but do not try to force and overtighten.

The KF system is convenient for users who need a fast leak tight system connection for their vacuum gauges. “KF” is short for Klein Flansche which is German for small flanges. Vacuum systems with KF flanges can reach into the 10^-8 Torr range. KF sizes, such as KF-16 and KF-25, are related to the maximum nominal inner diameter tubing in millimeters that can be attached to the flange.

Teledyne DV-6-KF-16 (Shown with o-ring assembly and clamp)

And lastly, ConFlat hardware is ideal for high vacuum and ultrahigh vacuum systems. ConFlat flanges have a knife-edge that seals against a gasket, usually copper. The connection is made by tightening a series of bolts; the number of bolts is a function of the size of the flange. Clean, baked, suitably pumped systems using ConFlat hardware have been known to reach pressures below 10^-13 Torr.

DV-6 Gauge Tube with ConFlat Flange

If you would like to discuss your application for vacuum gauges, mass flow meters, or mass flow controllers, we are standing by. You can reach us by phone (1-800-950-2468), email (hastings_instruments@teledyne.com) , or by using our LiveChat box at www.teledyne-hi.com or clicking on the box below.

Note: All photos of Swagelok fittings in this blog are used with their written permission.

This blog is the next installment in a series focusing on industrial gases. The first blog featured SF₆ and can be found here:   http://info.teledyne-hi.com/blog/sulfur-hexafluoride-gas-sf6 . The second blog focused on carbon dioxide (CO₂): https://info.teledyne-hi.com/blog/carbon-dioxide-co2 . Now we will take a look at Argon.

Argon (Ar) makes up just under 1% (0.93%) of the composition of air. Argon is odorless, tasteless, and has no color. It is a member of the noble gases. Science Notes (sciencenotes.org ) gives an interesting history of the term, “Noble gas”:

The term “noble gas” comes from a translation of the German word Edelgas, which means noble gas. German chemist Hugo Erdmann coined the phrase in 1898. Like a nobleman might consider it undignified to associate with commoners, noble gases tend not to react with other elements.

In any case, noble gases such as Argon are found in the right-hand column of the periodic table which means they have completed valence shells. The noble gases are generally monatomic and are mostly inert. The word “argon” comes from the Greek word “argos” which, according to Webster’s dictionary, means “idle, lazy.” This definition makes sense because Argon gas is quite unreactive and rarely forms compounds.

Because of its inert behavior, Argon gas has many uses. One of the most popular is the use of Argon as a cover gas when welding. A flow of Argon can provide an inert environment which prevents oxidation of welds and also allows the welder to have a more stable arc.

Argon is also used in the medical field. Argon plasma coagulation can be used to control tissue bleeding by injecting a jet of ionized argon gas. Also, since the physical probe does not have to actually touch the lesion, the procedure can be safer than other techniques. In ophthalmology, Argon lasers can be used to treat issues with the retina.

Many homes have double-pane windows filled with Argon gas. Argon provides better insulation than air because it allows less convection between the windowpanes. And because Argon is inert, it prevents deterioration of the window materials.

In lighting, an Argon glow discharge provides a pleasant purple-blue color. And in tungsten incandescent bulbs, a small amount of Argon is used to extend the bulb’s life.

Argon can also be used when making wine. In the wine’s casket or barrel, above the wine, is the headspace. Filling the headspace with Argon gas protects against oxidation and spoilage.

We could keep going in this blog and list many more applications. But we will stop this list with reference to a blog that we wrote back in 2018. The Emancipation Proclamation is stored in a double-paned encasement, designed by scientists at NIST, that that is mostly filled with Argon. You can read more here: https://info.teledyne-hi.com/blog/how-monitoring-instrumentation-is-helping-preserve-the-emancipation-proclamation

And, of course, when you need to measure Argon flow or vacuum levels with Argon, Teledyne Hastings is ready to help. Our flow instruments are able to measure and control flows from a few sccm (standard cubic centimeter per minute) up to several thousand slm (standard liters per minute).

Teledyne vacuum gauges are very good selection for use in Argon. The HVG-2020B (Click Here) is an excellent choice for measuring Ar from below 1 mTorr up to atmosphere. Convection driven pirani vacuum gauges, when used with gases other than N₂/air can have curious behavior as can be seen in the cartoon below.

The HVG-2020B vacuum gauge uses a gas-independent piezoresitive sensor that does not rely on convection affects and provides a more linear response to Argon across the entire measurement range.

If you would like more information about either the 300 Vue mass flow meters or controllers, or any of our vacuum gauges including the HVG-2020B, you can talk to any of our application engineers at 757-723-6531, email hastings_instruments@teledyne.com, or LiveChat with us at www.teledyne-hi.com

Special thanks to Lawrence Ferbee from the stockroom for his cartooning skills. If you would like to see Lawrence in action as he draws, check out our HVG-2020B video:

https://www.youtube.com/watch?v=_Bk3Q7SpSUc

A Pirani vacuum gauge is a type of thermal conductivity gauge that is also often referred to as a “thermal heat transfer gauge”. In a Pirani gauge, the rate of heat transfer is a function of the number of gas molecules present in the vacuum system. Pirani gauges are capable of providing reliable pressure measurement in a wide variety of vacuum technology applications.

What is the working principle of the Pirani Vacuum Gauge?

A Pirani vacuum gauge contains a heated component, such as a wire or thin-film membrane (see figure on right), which is brought to an elevated temperature, typically through the use of a bridge circuit. As changes in gas molecular density occur, the transfer of heat from the wire to the gas is affected. This heat loss is dependent on gas type and pressure, and the amount of energy required to keep the wire at temperature varies accordingly. Consequently, the amount of energy is dependent on vacuum pressure and can be converted to a pressure value.

Accurate pressure measurement depends on the ability of the bridge circuit to maintain very precise control of the sensor’s temperature. The most common technique is to use a Wheatstone bridge circuit. In one design of a Pirani bridge circuit, two legs of the bridge are controlled at the same voltage via an electronic feedback loop. The measurement technique then is to quantitate the power required to maintain the heated sensor at a given temperature above ambient. (See J. Vac. Sci. Technol. A 13(6), Nov/Dec 1995)

In the case of a gauge that employs a heated sensor wire, there are three main heat loss routes: bulk thermal conduction via the wire and its supports, radiation losses, and thermal conduction losses through the gas. It follows that a well-designed Pirani vacuum gauge minimizes loss of signal due to radiation and bulk thermal conduction. Radiation losses are strongly (fourth power) dependent on the temperature of the heated sensor. Consequently, when operating a Pirani gauge, it is important to keep the sensor at a low enough temperature such that the radiation loss mechanism does not dominate the overall signal. Similarly, a well-designed Pirani gauge minimizes bulk thermal conductivity via the sensor element. For both radiation and bulk thermal conductivity losses, the loss factors are dependent on temperature.

What are the advantages of the Pirani Vacuum Gauge?

The Pirani vacuum gauge offers numerous advantages. Foremost, the gauges are typically very easy to use and can provide years of trouble-free, reliable pressure measurement, because they have no moving parts. Additionally, they are highly economical, costing far less than capacitance manometers. Flexibility in output monitoring includes local displays, analog output, and/or digital communication. Pirani vacuum gauges are relatively fast and are very responsive to changes in the vacuum system’s pressure. Gauges with very small internal dimensions can offer increased response speed. It should be noted that convection-enhanced Pirani vacuum gauges require larger volumes to support convection currents and may therefore have slower response, simply due to the larger volume that must be evacuated inside the tube. Convection-enhanced Pirani vacuum gauges measure pressure up to atmospheric pressure, however, their accuracy in gases other than air or nitrogen at elevated pressure, can be very poor.

Combination gauges, such as Teledyne Hastings’ HVG-2020B, combine a piezo-based sensor with a conventional, thermal-based Pirani sensor to provide accurate pressure measurement from 10-4 Torr (0.1 mTorr) to 10+3 Torr.  Additionally, by combining the two technologies in one gauge, the errors associated with the gas composition specific Pirani sensor are eliminated at pressures above 10 Torr.

What are some of the applications for Pirani Vacuum Gauges?

Many Pirani vacuum gauges measure pressure from below 1 mTorr up to atmosphere and are a very good choice for a wide variety of applications:

• Pirani vacuum gauges are used to monitor the pump down from atmosphere to the start of the high vacuum region (where turbomolecular pumps or other high-vacuum pumps take over)
• In the vacuum metallurgy industry (high-purity alloys manufactured in a controlled environment) Pirani vacuum gauges ensure process consistency and optimization of different thin-film coating systems.
• Freeze dryers and vacuum dryers frequently operate in a vacuum region that is well-suited to Pirani vacuum gauges, as well as the manufacture and maintenance of cooling systems (air conditioning, ice machines, and refrigeration).
• Various analytical instrumentation requires vacuum levels in and below the mTorr region, and the Pirani gauge is often the most cost-effective instrument for these applications.
  

FAQs

What are some best practices for Pirani Vacuum Gauges?

Pirani gauges have no moving parts and generally do not require maintenance. It should be noted that this type of gauge is susceptible to contamination, especially in oil-based pumping systems. In systems with contamination, the gauge tube should be installed with the port facing downward to reduce oil accumulation inside the tube. 

Convection-driven Pirani vacuum gauges should always be installed with the cylindrical axis parallel to the floor. Failure to install this type of gauge properly will lead to erroneous readings above the rough vacuum level. 

If the vacuum system has excessive oil vapor or other contaminants, a molecular sieve filter can be used to extend the service life of the gauge.

For information on Teledyne Hastings Vacuum Gauges, visit https://www.teledyne-hi.com/products-services/vacuum-measurement-and-control or click the button below to contact us for more information.

What is a Thermocouple Gauge?

Teledyne Hastings was founded in 1944 as “The Hastings Instrument Company” by Charles and Mary Hastings. The introduction of thermal sensing technology in late 1940s at the young company offered potential for a variety of new technologies and quickly became the foundation for many early Hastings’ instruments. Early products included air velocity indicators, thermal mass flow meters, stack emission monitors and, of course, the thermocouple vacuum gauge tube.

By 1964, Hastings Instruments had grown into one of the leading vacuum and thermal mass flow instrument companies in America. Today, our popular Thermocouple Vacuum Gauge Tube product lines, including the DV-4, DV-5, and DV-6, are trusted globally where repeatable, rugged, and dependable pressure measurement is needed. Based in Hampton, Virginia for over 75 years, the highly-skilled employees at Teledyne Hastings are dedicated to delivering thermocouple vacuum gauges of exceptional quality.

How does a thermocouple gauge tube work?

The physics behind how a thermocouple vacuum gauge tube functions is simple. For example, let’s look at the DV-6R thermocouple vacuum gauge tube, which is capable of pressure measurements within the range of 0 – 1000 mTorr. The DV-6R can be seen in the image below, along with the representative schematic.

A thermocouple consists of a junction of two dissimilar filaments that are soldered together. Three thermocouples are shown (A, B, and C) in the DV-6R diagram, and many thermocouple gauge tubes use multiple thermocouples to form a thermocouple array. At each junction, there is a small voltage (on the order of a mv) which is a function of temperature. When the gauge tube is in operation, thermocouples A and B are resistively heated inside the gauge tube’s housing. Because each filament connected to both A and B thermocouples is exposed to the gas in the vacuum, thermal energy is transferred away from the array at a rate which is dependent on the number of collisions between the gas molecules and the filament wires.  This transfer of thermal energy is, in turn, dependent on the pressure inside the tube. In essence, by measuring the rate of thermal energy transfer, the pressure inside of the tube is indirectly determined!

To understand the concept more fully, let’s consider two extremes. In high vacuum, where the pressure is very low, there will be fewer gas molecules to collide with each filament and the tube’s voltage output will be relatively high. Higher temperature corresponds to higher thermocouple output. As we approach near atmospheric pressure (760 torr), there are more gas molecules, resulting in more thermal energy transferred away from the filament. Consequently the thermocouples run at a lower temperature resulting in a relatively low output. The varying output produced by the thermocouple gauge is dependent on the thermal conductivity of the gas in the vacuum system, which is then used to measure pressure.

Thermocouple vacuum gauges are “indirect gauges”, meaning they accomplish pressure measurement by measuring a physical property, such as thermal conductivity or ionization rate of gas molecules, to determine the pressure in a vacuum system.

How to use a thermocouple vacuum gauge tube:

Teledyne Hastings’ vacuum gauge tubes are manufactured to the highest quality and tested to be extremely repeatable from one gauge tube to another to ensure accurate process control. Thermocouple vacuum gauge tubes are physically installed on a vacuum system and then used to measure various pressures across the tube’s full scale range. When the filament inside the tube is excited, the output is then converted to a pressure measurement.

An example gauge tube installation would consist of a DV-6R thermocouple vacuum gauge tube connected to a DCVT-6 panel meter or HPM-4/5/6 handheld meter. Both the DCVT-6 and HPM-4/5/6, are factory configured to work seamlessly with DV-6R gauge tubes, out of the box. The output from the gauge tube is then monitored by the DCVT-6 or HPM-4/5/6 and the level of vacuum displayed.

In the case of the DCVT, two contact relays are available for process control, and the dual relays will independently toggle according to user-defined setpoints, when the vacuum setpoint has been crossed. This demonstrates how the factory-tested repeatability of our gauge tubes results in consistent and repeatable process control! The DCVT also provides serial communication (RS232), LabVIEW™ drivers and linearized analog output options (0-1 VDC, 0-5 VDC, 0-10 VDC, 4-20 mA).

Related Products

Teledyne Hastings' Vacuum Products
DCVT-6	HPM 4/5/6	DV-6R	DV-6S

Application Example:

There are numerous, diverse vacuum applications and different vacuum systems can require specific thermocouple vacuum gauge tubes. At the most basic level, vacuum systems can be installed in a variety of environments including outdoor with exposure to weather elements, indoor industrial and laboratory conditions in which exceptionally high cleanliness standards are required.

A good example of how a thermocouple vacuum gauge tube meets the requirements of a specific application, is presented in the vacuum insulation or vacuum jacketing field. The technique of using a vacuum guard or barrier to thermally insulate a cryogenic or refrigerant tank is straightforward: by removing the air from around an object, conductive heat transfer is eliminated. The better the vacuum attained, the higher the level of vacuum insulation. To effectively measure pressure below the 1 Torr range, a vacuum dial gauge is simply not sensitive enough; a thermocouple vacuum gauge tube is required.

To obtain vacuum readings from DV-6 gauge tubes, a dedicated electronic display or handheld battery-operated readout is used. The Teledyne Hastings’ DCVT provides continuous monitoring via an easy to read LED display. For periodic vacuum monitoring of one or more tubes, the hand-held HPM 4/5/6 is recommended because of its portability (9V battery power) and its ability to be quickly connected to a DV-6 tube and obtain an accurate reading with fast response time. To ensure the most accurate measurement, the DB-20 Reference Tube can be used to validate the electronic calibration. This can assist in determining if the thermocouple vacuum gauge tube requires replacement by ensuring that it is producing an accurate reading.

Teledyne Hastings has created a detailed application note on vacuum jacketing insulation at this link.

For more information about any of our thermocouple sensor series or vacuum gauges, we are here to help. In addition to LiveChat on our website, you can contact us at hastings_instruments@teledyne.com or call 757-723-6531 (800-950-2468) or click the button below.

March is Women’s History Month and this year we’d like to focus on Mary Hastings, one of the key founders of Hastings Instruments. Mary Comstock graduated from William & Mary with a degree in physics with minors in math and chemistry. She was truly a pioneer in many ways. After college, she took a job as a “computer” at NACA (National Advisory Committee for Aeronautics) in Hampton, Virginia. There, Mary met Charles Hastings, a young engineer who had his office across the hall from her. The two were married in 1940.

In a business era that was almost thoroughly dominated by men, Mary was an invaluable contributor to the success of Hastings Instruments. She promoted the fledgling company through press releases that she prepared for local papers and thereby helped to secure critical financial support. She attended shareholder meetings of other companies to learn how they conducted their annual meetings. For many years, Mary prepared the annual report for Hastings shareholders. In short, she was not afraid to tackle any challenge that would help grow the company. Moreover, Mary was a constant voice of wisdom to her husband with respect to company decisions and policy. She accomplished all of these things while the couple raised three children.

It is reasonable to assume that without Mary Hastings, the company would not have been nearly as successful. So during Women’s History Month, we want to celebrate her many accomplishments. You can hear more about Mary from her daughter Carol Hastings Sanders in this video:

https://www.youtube.com/watch?v=AxdFQQXEEzQ

Happy Valentine’s Day 2021! Time for me to run out and order some freeze-dried flowers for my wife. What?... yes, it’s true! In case you have not heard of this, freeze-dried flowers can make a beautiful gift.

According to Flowers Forever – Bellabeads of Columbia SC, https://myflowersforeverjewelry.com/pages/freeze-dried-flowers, freeze-dried flowers will, “retain their beauty as if frozen in time as a lasting memento.” They can be placed in shadow boxes or frames and stored for many years.

So this is probably the best time to tell you about this fun application of vacuum technology. I recently worked with one of our vacuum customers who services freeze driers for florists, so this topic is “fresh” in my mind. Freeze drying is well-known for use in the manufacturing of food and drugs. Most likely, you have something in your house that has been processed with freeze-drying. So, let’s take a closer look.

Freeze drying, also known as lyophilization, is a process in which water molecules are removed from biological cells without damaging the cell structure. For starters, the product to be freeze-dried is chilled and the water inside is completely frozen (i.e. placed in the solid state). Next, the pressure is reduced using vacuum pumps and the water molecules sublimate – that is, water goes from the solid phase directly to the gas phase.

The gas load due to the water vapor is usually very high and requires condensers to trap the liberated water and stop it from overwhelming the pumping system. Commercial freeze driers (see image below) include a heat exchanger which serves two purposes: first, the heat exchanger is used to cool the product and later, it is used to gently heat the product to drive the water sublimation.

View inside commercial freeze-drier

Do you know of some other cool applications of vacuum technology, we would “love” to hear from you! Please visit Live chat with us at www.teledyne-hi.com or call 1-800-950-2468.

Special thanks to Flowers Forever – Bellabeads for the use of flower image from their beautiful website.

This blog is the next installment in a series of blogs focusing on industrial gases. The first blog featured SF₆ and can be found here:   https://info.teledyne-hi.com/blog/sulfur-hexafluoride-gas-sf6 In this blog, we will explore one of the most useful, and well-known, of the industrial gases, carbon dioxide (CO₂).

CO₂ is an odorless and colorless gas. As a matter of fact, you exhale about a quarter liter of CO₂ every minute (https://www.nytimes.com/1990/08/14/science/q-a-burden-of-breathing.html). And while we are on the subject of breathing, it is interesting to note that it is usually the buildup of CO₂ that triggers a breath, not the lack of oxygen. A recent special feature in Gasworld US Edition noted that “low concentrations are not harmful, higher concentrations can affect respiratory function, cause excitation and depression of the central nervous system.”

The structure of CO₂ is linear. The electronic structure of the molecule features bonding pairs of electrons around the central carbon atom. These electron pairs repel equally while bonding to oxygen atoms. The equal repulsion is what gives CO₂ its linear arrangement. A diagram of the molecule is shown on right.

There are many fascinating uses of CO₂, some are well-known while others may be new to the reader.

• Used in industry to produce chemicals and as feedstock
• Used in the metals industry to improve the hardness of castings
• Often used as a carrier for spraying of paints or for spraying vegetable oils in cooking
• Liquid CO₂ can be used as a solvent in eco-friendly dry cleaning
• Solid CO₂ can be used for cold storage
• Jets of CO₂ are used for special effects in movies, live shows, and amusement parks
• Gas phase CO₂ is used for fire extinguishers
• Carbonated beverages

A quick note on purity... CO₂ used for fire extinguishers can be ~ 95% pure. However, the purity of CO₂ in carbonated beverages can be as high as 99.9995%.

A word on explosive decompression of elastomers when using CO_2. CO₂ is known to more easily penetrate elastomeric seals such as o-rings and diaphragms at pressures significantly higher than atmosphere which in turn can cause the host material to swell. If the pressure is suddenly decreased (i.e rapid decompression), the internal gas can rupture the elastomer and the seal can be compromised. There are a few things the user can try to reduce risk. First, select materials that are less susceptible. Viton® is often not a good choice for CO₂ applications. Second, if the application will allow, try to reduce the amount of time the elastomeric seal is held at elevated pressure. And third, when the pressure is reduced, allow more time for the CO₂ to exit the material.

Flow controllers from Teledyne Hastings are used to measure and control CO₂ flow in many of the aforementioned applications. The 300 Vue can provide all-metal seals and Kalrez® valve seat. (see diagram below). For users of the elastomeric-sealed 200 Series, we recommend Buna-N seals which are less susceptible to explosive decompression.

Teledyne vacuum gauges can be used with CO₂. The HVG-2020B (Click Here) is an excellent choice for measuring CO₂ from below 1 mTorr up to atmosphere. Convection driven pirani vacuum gauges, when used with gases other than N₂/air can have curious behavior as can be seen in the cartoon below.

The HVG-2020B vacuum gauge uses a gas-independent piezoresitive sensor that does not rely on convection affects and provides a more liner response to CO₂ across the entire measurement range.

If you would like more information about either the 300 Vue mass flow meters or controllers, or any of our vacuum gauges including the HVG-2020B, you can talk to any of our application engineers at 757-723-6531, or email hastings_instruments@teledyne.com or LiveChat with us at www.teledyne-hi.com

Special thanks to Lawrence Ferbee from the stockroom for his cartooning skills. If you would like to see Lawrence in action as he draws these, check out our HVG-2020B video:

https://www.youtube.com/watch?v=_Bk3Q7SpSUc

Viton® is a registered trademark of DuPont Performance Elastomers

Kalrez® is a registered trademark of DuPont Dow Elastomers