Category Archives: Technical Information

Temperature Sensor Design

Temperature Sensor Design From Peak Sensors

Calculating and producing effective temperature sensor design can be a tough challenge. Luckily the experts at Peak Sensors are on hand to help you by offering free advice, without all the pushy sales talk.

A signpost representing advice, support and help for temperature sensor design.

We can help point you in the right direction

Important Things to Consider When Designing Temperature Sensors

Below is a list of important factors to consider when partaking in temperature sensor design.

  • How accurate must the sensor be?
  • What is the budget to produce the design?
  • What connection demands, if any, are there?
  • What is the temperature of the application?
  • How big will the probe need to be.

Probe Accuracy

You should consider carefully the accuracy that your new temperature sensor will require. Typically sensors will fully enter a process and be surrounded by the measured medium.However often pipe external surface locations are all that is available. Surface measurements can be made more accurate through improved surface area thermal contact or good insulation design. Clearly the cost is affected by reading quality improvements.

Temperature Sensors are available in different nominal accuracy bands. The tighter tolerance bands cost more. Probes can be calibrated to determine accuracy but again cost is incured by doing so.

Process Connection

Probes need to be securely installed into an application. Often this will provide a pressure seal, a means of replacement, immersion control, enhance a thermal contact or other functions. Standard techniques include compression fittings, flanges, clips etc.

Temperature Range

The overall possible temperature range will play a major part in specifying the sensing technology employed. Each type of temperature sensor has a set temperature range at which it will perform:

  • Thermocouples cover the widest temperature range, but are non linear devices, they can be very expensive at higher temperatures and when used at extremes suffer from thermal drift.
  • Resistance thermometers have a more limited range, but are more accurate than thermocouples. They are linear variable resistors. Novel instrumentation can easily process the signal.
  • Thermistors can be very cheap sensors. Most are non linear. The range is even more limited than Resistance Thermometers.

Size Constraints

Thermocouples can be very small and still robust. With designs produced down to around 0.25mm in length. Thermistors and Resistance thermometers are larger in size, with a minimum width of around 2mm.

Probe Environment

Sensors must withstand the application environment. This usually involves a secondary protective sheath. Stainless Steel is often employed. Common grades include:

  • 316SS
  • 310SS,
  • 446SS
  • 321SS

Nickel alloys can also be used for higher temperature applications. It is important to remember that many temperature sensor design ideas fail because the important sensor element is not protected heavily enough against the environment.

Signal Generation and Transmission

Thermocouple Signals are provided in micro or milli volt outputs. The signal is always vulnerable to pickup or other interference whilst in the application. Transmitters can convert sensor signals to 4-20mA robust signals. For significant plant transmission.  wireless transmission can be used. We know and understand which transmission type is needed for each industrial application.

We are experts in Temperature Sensor Design

There are so many considerations that need to be evaluated during temperature sensor design. The team at Peak Sensors have the skill set and the experience to help you build your new temperature sensor design.

Identifying Temperature Sensor Type

Identifying Temperature Sensors

We often receive phone calls from potential customers who have a temperature sensor in their hands, but little other information about it. This presents us with a number of problems. The first issue is identifying exactly what type of sensor it is.

identify a temperature sensor, a looking glass being held by a hand

 Most industrial plant contact temperature sensors are thermocouples, resistance thermometers or thermistors. To identify the type of sensor, our advice goes along the lines of:

  1. Is there any visible information on the instrument that displays the temperature?
  2. What temperatures are usually recorded?
  3. How many and what colour are any wires on the sensor or subsequent cabling?
  4. Disconnect the sensor from the system and take a resistance measurement across any terminals on the sensor with a multimeter.

 Step 1 Instrumentation Information

This may not be straightforward due to Jargon. Possibilities are:

  • Type K Thermocouple. This may also be refered to as NiCr v NiAl, NiCr v Ni, T1 T2. Type K is the most common thermocouple type.
  • Type J Thermocouple. Known as Iron Con, or Fe v Con.
  • Type N Thermocouple. Nicrosil v Nisil.
  • Type R Thermocouple. Often called Pt v Pt13%Rh.
  • Type S Thermocouple. Also known as Pt v Pt10%Rh
  • Type B Thermocouple. Also revered to as Pt6%Rh v Pt30%Rh
  • Resistance thermometer. Also known as Pt100, RTD, Pt1000 or simply RT
  • Thermistors may be referred to an NTC, PTC or simply as nominal ohmic value such as 10kΏ. The range of resistance possibilities is very wide.

There are also a range of other less common sensor assemblies which exact but are extremely rare.

 Step 2 Temperature Sensor Range

The temperature sensor range that each sensor type can work at can hold vital information as to which sensor the customer is currently using. The usual maximum temperatures of sensors can be summarised as below, however it is not an absolute limit and individual designs can have other limitations.

Sensor Type Common limit
K 1100°C
J 800°C
N 1200°C
R 1500°C
S 1500°C
B 1600°C
RTD 500°C


Step 3 Quantity and Colour of Wires.

Colour codes can identify a sensor. If there are 2 wires, it could be any type of sensor. The options on Thermocouple colours are summarised here

On top of that, a red and white wire will usually signify a resistance thermometer. American (ANSI) colour codes is another possibility and a summary can be found here

If there are 3 wires, two red and one white, it is almost certainly a 3 wire Resistance thermometer. A third wire could also be a sheath grounding wire, while the other two are a thermocouple.

If there are 4 wires, two red and two white, it is probably a 4 wire resistance thermometer. Any other colours can be again cross checked with the above tables as you are probably looking at a duplex thermocouple with two measuring points.

Step 4 Physical Readings

This requires some disassembly and should only be done by experienced, authorised personnel. A resistance reading across the sensor terminals can be decisive. Assuming the temperature sensor is quite small (less than say 1 Meter long) a very low resistance reading at any temperature (less than 10 Ώ) will indicate that it is a thermocouple. Around 110Ώ at room temperature will almost certainly be a Pt100, or 1100Ώ at room temp a Pt 1000. A much higher resistance at room temperature is probably a thermistor. Open circuit readings simply indicate that the sensor is broken, and you probably knew that anyway.

We hope that by following this step by step guide, you should find it easy to identify your temperature sensor or assist others to do so.

Learn how you can identify a temperature sensor based on it's properties. A keyboard with green background and identify written on it.

You should now find it easier to identify different temperature sensor types