Wednesday, December 12, 2018

Happy Holidays from Duro-Sense!

From all of us at Duro-Sense, we wish our customers, partners and vendors a safe and happy holiday season and a wonderful 2019!


Monday, December 10, 2018

Duro-Sense a Critical Partner in Hydrogen Contamination Detector

We take for granted the gasoline (or diesel) we put in our cars and trucks is free from contaminants when pumped in to our gas tanks. The purity we've come to expect at the fuel pump didn't happen overnight. It took many years, and thousands of engineering hours, to develop the refining processes that produces today's clean gasoline and diesel. 

Fuel Cell Vehicles are a category of electric vehicle (EV's). Fuel cell vehicles use hydrogen gas (H2) to power an electric motor. Unlike conventional vehicles which run on gasoline or diesel, fuel cell cars and trucks combine hydrogen and oxygen to produce electricity to drive the motor. 

Similar to the path that gasoline and diesel processing took toward purity, the use of H2 as feedstock for fuel cells in transportation has driven requirements for H2 purity standards to very strict levels. This push has also elevated the need for cost-effective and reliable instruments that can sample H2 near the nozzle of a delivery pump, and either certify acceptability or provide a signal to shut off the fuel distribution system.

Duro-Sense Corporation, a California based manufacturer of high quality temperature sensors, is part of a team working under a DOE funded research program to develop a Hydrogen Contamination Detector. The sensor, which will be installed at hydrogen fueling stations, will detect poor quality hydrogen gas before entering the fuel cell vehicle. The sensor is intended to detect multiple impurities at extremely low levels in hydrogen to prevent fuel cell performance degradation. 

Duro-Sense is designated as the industrial partner and vendor aiding in defining the commercial manufacturability of the Hydrogen Contamination Detector. 

As part of their preliminary work, a thermocouple embodiment was selected as a cost-effective platform for the Hydrogen Contamination Detector because:
  • Direct Commercial Availability
  • Proven History of Reliability and Robustness
  • Adaptability of Conductor Materials for Most
  • Appropriate Catalyst for Each Contaminant
  • Ability to Incorporate up to 12 Conductors a Single Thermocouple, Reducing Fluid Stream Penetrations
They also assisted with a high pressure pass-through to integrate the sensor into fluid stream to accommodate a pressure rating of 30,000 PSI using a cone and thread style fluid connection.

The Hydrogen Contamination Detector project is still in its very early stages, and research and development continues, subject to funding and continued interest in alternative fuel technology.

For more information, contact Duro-Sense at 310-533-6877 of visit their web site at https://duro-sense.com.

Tuesday, December 4, 2018

3 Bottom Line Criteria to Help You Choose Between Thermocouples and RTDs

Temperature Sensor Selection Criteria
Both RTD and thermocouple probes monitor temperature but which one is right for your application?

The first question to ask yourself is what is the temperature range you are trying to monitor?
Generally, if the temperature is above a hundred and fifty degrees Celsius, a thermocouple would be used. For anything below a hundred and fifty degrees Celsius, an RTD would be used.

The next question to ask is what is the required sensor accuracy? 
RTDs provide more accurate readings with repeatable results, this is why RTDs are typically used when temperatures are within its monitoring range.

The last question is what is the purchase budget and how many do you need?
Thermocouples can be up to three times less expensive than RTD probes making thermocouples a good choice when purchasing a large quantity or when the budget is tight

These three criteria are VERY basic, and intended just to point you in the right direction. There are many other differences between thermocouples and RTDs that need to be understood before application.  Always consult a temperature sensor application expert prior to installing or specifying a thermocouple or RTD where failure can cause harm.

Duro-Sense Corporation
https://duro-sense.com
(310) 533-6877

Wednesday, November 28, 2018

Best Practice for Mounting Thermocouples in Pipes

not recommended
Diagram 1 - Not recommended.
Immersion type thermocouples are used to measure the temperature of liquid flowing in a pipe or sitting in a vessel. The particular orientation for any installation depends on the application, whether additional hardware is required, and the relative dimensions of the thermocouple sheath and the pipe.

There are however, recommended practices for placing thermocouples in the piping flow stream.

As you can see from diagram 1, placing the thermocouple in a tee, positioned perpendicular to flow is not recommended. This is because the conduction along the sensing area may be non-negligible and could bias the measurement, depending on the liquid and ambient temperatures. In addition it may be hard to know precisely where the measurement junction is located along the cross section of the pipe in this configuration.

Ideally they should be mounted in a tee where an elbow would normally be used as you see in diagram 2. If possible the thermocouple should be oriented along the normal flow direction, and the measurement located downstream of the T-bend (the T will help mix the liquid if it is not thermally uniform).
recommended
Diagram 2 - Recommended orientation.
If there is no convenient spot where an elbow would normally be used, a u-shape can be adapted to allow the installation for the tee. See diagram 3.

U shape
Diagram 3 - Use U shape if there is no convenient placement for a tee.
For more information, contact Duro-Sense by calling 310-533-6877 or visit their web site at https://duro-sense.com.

Friday, November 9, 2018

Platinum Resistance Temperature Detectors

Platinum Resistance Thermometers Detectors (RTDs) rely on the fact that platinum, like many other metals, exhibits increased electrical resistance as temperature rises. For example, a conventional RTD designed to provide 100 Ohms at 0 °C has a resistance in the neighborhood of 80 Ohms at -50 °C and 120 Ohms at 50 °C, or a sensitivity of about 0.4 Ohms per degree. RTDs constructed to particularly exacting specifications, termed Standard Platinum Resistance Thermometers, are named as the defining measurement tools for interpolating temperatures under ITS-90. In general, RTDs can have high accuracy (0.01 °C), stability, and repeatability across a wide range of temperatures from -200 °C to 500 °C.

Typically the platinum element is formed into thick or thin films, or the platinum wire is arranged in two, three or four helical coils (see diagram, right) – the more coils, the higher the sensitivity. The film or wire is placed inside a glass or ceramic enclosure, and can be supported by loose or compacted MgO. Platinum-based leads connect the probe unit to the thermometer electronics, which convert the electrical signal to temperature.

RTDs are broadly divided into two groups: Industrial RTDs and Standard Platinum Resistance Thermometers, depending on sensitivity and robustness. ASTM and IEC define several classes of RTDs, each with a different set of specifications. An ASTM "Class A" unit, for example, has an out-of-the-box tolerance — maximum permissible error — that ranges from 0.47 °C at -200 °C to 0.13 °C at 0 °C to 0.98 °C at 500 °C.

Advantages

  • Wide temperature range
  • Resistance-temperature relationship is well characterized.
  • Rugged construction in industrial RTDs
  • Available in different shapes and sizes – application specific
  • Can be used with a digital temperature read-out device.

Disadvantages

  • Mechanical shock and vibration will cause drift.
  • Deterioration at elevated temperatures (e.g., >500 °C)
  • 2-and 3-wire devices need lead-wire compensation.
  • Non-hermetically sealed RTDs will deteriorate in environments with excessive moisture.



Post abstracted from "Mercury Thermometer Alternatives: Platinum Resistance Thermometers (PRTs)" by NIST.

Wednesday, October 31, 2018

Thermocouple Extension Wire

In every thermocouple circuit there must be both a measurement junction and a reference junction: this is an inevitable consequence of forming a complete circuit (loop) using dissimilar-metal wires. As we already know, the voltage received by the measuring instrument from a thermocouple will be the difference between the voltages produced by the measurement and reference junctions.

Since the purpose of most temperature instruments is to accurately measure temperature at a specific location, the effects of the reference junction’s voltage must be “compensated” for by some means, either a special circuit designed to add an additional canceling voltage or by a software algorithm to digitally cancel the reference junction’s effect.

In order for reference junction compensation to be effective, the compensation mechanism must “know” the temperature of the reference junction. This fact is so obvious, it hardly requires mentioning. However, what is not so obvious is how easily this compensation may be unintentionally defeated simply by installing a different type of wire in a thermocouple circuit.

To illustrate, let us examine a simple type K thermocouple installation, where the thermocouple connects directly to a panel-mounted temperature indicator by long wires:




Like all modern thermocouple instruments, the panel-mounted indicator contains its own internal reference junction compensation, so that it is able to compensate for the temperature of the reference junction formed at its connection terminals, where the internal (copper) wires of the indicator join to the chromel and alumel wires of the thermocouple. The indicator senses this junction temperature using a small thermistor thermally bonded to the connection terminals.

Now let us consider the same thermocouple installation with a length of copper cable (two wires) joining the field-mounted thermocouple to the panel-mounted indicator:


Even though nothing has changed in the thermocouple circuit except for the type of wires joining the thermocouple to the indicator, the reference junction has completely shifted position. What used to be a reference junction (at the indicator’s terminals) is no longer, because now we have copper wires joining to copper wires. Where there is no dissimilarity of metals, there can be no thermoelectric potential. At the thermocouple’s connection “head,” however we now have a joining of chromel and alumel wires to copper wires, thus forming a reference junction in a new location at the thermocouple head. What is worse, this new location is likely to be at a different temperature than the panel-mounted indicator, which means the indicator’s reference junction compensation will be compensating for the wrong temperature.

The only practical way to avoid this problem is to keep the reference junction where it belongs: at the terminals of the panel-mounted instrument where the ambient temperature is measured and the reference junction’s effects accurately compensated. If we must install “extension” wire to join a thermocouple to a remotely-located instrument, that wire must be of a type that does not form another dissimilar-metal junction at the thermocouple head, but will form one at the receiving instrument.

An obvious approach is to simply use thermocouple wire of the same type as the installed thermocouple to join the thermocouple to the indicator. For our hypothetical type K thermocouple, this means a type K cable installed between the thermocouple head and the panel-mounted indicator:


With chromel joining to chromel and alumel joining to alumel at the head, no dissimilar-metal junctions are created at the thermocouple. However, with chromel and alumel joining to copper at the indicator (again), the reference junction has been relocated to its rightful place. This means the thermocouple head’s temperature will have no effect on the performance of this measurement system, and the indicator will be able to properly compensate for any ambient temperature changes at the panel as it was designed to do. The only problem with this approach is the potential expense of thermocouple-grade cable. This is especially true with some types of thermocouples, where the metals used are somewhat exotic (e.g. types R, S, and B).

A more economical alternative, however, is to use something called extension-grade wire to make the connection between the thermocouple and the receiving instrument. “Extension-grade” thermocouple wire is made less expensive than full “thermocouple-grade” wire by choosing metal alloys similar in thermo-electrical characteristics to the real thermocouple wires within modest temperature ranges. So long as the temperatures at the thermocouple head and receiving instrument terminals don’t get too hot or too cold, the extension wire metals joining to the thermocouple wires and joining to the instrument’s copper wires need not be precisely identical to the true thermocouple wire alloys. This allows for a wider selection of metal types, some of which are substantially less expensive than the measurement-grade thermocouple alloys. Also, extension-grade wire may use insulation with a narrower temperature rating than thermocouple-grade wire, reducing cost even further.

Extension-grade cable is denoted by a letter “X” following the thermocouple letter. For our hypothetical type K thermocouple system, this would mean type “KX” extension cable:



Thermocouple extension cable also differs from thermocouple-grade (measurement) cable in the coloring of its outer jacket. Whereas thermocouple-grade cable is typically brown in exterior color, extension-grade cable is usually colored to match the thermocouple plug (yellow for type K, black for type J, blue for type T, etc.)

For more information on thermocouple extension wire, contact Duro-Sense by visiting https://duro-sense.com or by calling 310-533-6877



Reprinted from "Lessons In Industrial Instrumentation" by Tony R. Kuphaldt – under the terms and conditions of the Creative Commons Attribution 4.0 International Public License.