Active temperature measurement is as diverse as passive temperature measurement. That is why there are many different types of active thermocouples as well.
What the difference between active and passive thermocouples is, what advantages it brings you to use an active thermocouple and what you have to pay attention to in the selection, purchase, installation and operation, we have compiled for you in this guide.
What is an active thermocouple?
If a thermocouple and a transmitter are used as a permanently or flexibly connected assembly, this is also referred to as an active thermocouple. We offer you a thermocouple and a suitable transmitter as a set. This has the advantage that in case of a defect only one component can be exchanged. Nevertheless, you can be sure that both work optimally together.
Passive thermocouples are thermoelectric sensors with two wires made of different materials. These are connected together at one point (measuring point) and you can measure a thermoelectric voltage at their ends (reference junction), which also changes when the temperature changes. This thermoelectric effect is also called Seebeck effect. Thermocouples measure the temperature difference between measuring point and reference junction, i.e. the temperature at the reference junction must be known.
The output signal is a thermoelectric voltage, which is then translated by the measuring electronics. The passive probe does not require an external supply voltage.
With active thermocouples, the thermoelectric voltage is not output.
Instead, the transmitter ensures that a standardized output signal is output as a voltage in mA or as a current in V. This means that the thermocouple can now be used on many standard devices.
The use of a transmitter has further advantages:
- longer distances can be bridged
- the output signal is amplified
- the output signal is standardized and can be used on many devices
- depending on the transmitter type, malfunctions such as cable breakage or incorrect connection of the probe can be detected if necessary.
- There is also a disadvantage: active probes need a supply voltage or current to convert the signal.
The most important thing is that the probe is a good match for the intended measurement task. You can find out with these questions:
- In which medium is to be measured?
- How is the measurement to be made (plunge measurement, surface measurement ...
- Which process connection is required, i.e. how is the probe to be installed?
- In which temperature range should the measurement take place
- How fast does the measurement have to take place?
- Are there any other influencing factors, such as protection class, steam, vibration, etc., that affect the temperature probe?
In our online store you can buy sets of cable thermocouples with stainless steel sleeve or screw-in thermocouples with screw connection in G1/2", G3/8", G1/4", M4, M6 and M8 as Type J or Type K in a set with the matching Hat rail transmitter (as active thermocouples). If you need a different type of probe or also a different transmitter shape e.g. in the housing, please feel free to contact us - we will feel free to check for you what we can offer.
Active thermocouples are a measuring system consisting of two components. Therefore the accuracy, response time and tolerance of the whole system must be considered. For both components, the operating conditions such as permissible measuring and operating range temperatures and protection class must be observed.
How does an active thermocouple work?
An active thermocouple consists of two components: the thermocouple, which detects the thermoelectric voltage, and a temperature transmitter, which converts it into a standardized output signal: either in amperage - in which case the output is in amperes (mA) or in voltage - in which case the output is in volts (V). Which output signal should be selected depends on how and with which device the output signal is to be further processed.
What are the advantages of using an active temperature probe?
Active thermocouples are somewhat more expensive than passive ones. This is why they are used, for example, in difficult ambient conditions or for more difficult requirements. With active probes, the output signal can be standardized and amplified. This means that the signal can be transmitted reliably over longer distances and the measuring point and the evaluation point can be (spatially) far apart without, for example, line resistances falsifying the result. In addition, faulty measurements can be detected. In many areas of measurement technology, a certain standardized output signal is required in order to process the measurement data. This is provided by active probes.
For which applications do I need an active thermocouple?
Typically, active thermocouples are used in heating technology, building services engineering, air conditioning technology or plant engineering. They measure the temperature of air or a liquid medium as an immersion measurement or as a surface measurement, which is then fed into different control systems.
You need an active thermocouple if you require a signal between 4 to 20 mA or in 0 to 10 V for further processing, if you want to bridge longer distances between the measuring point and the evaluation unit or if you want to ensure and permanently monitor that a measuring signal arrives.
You must pay attention that you need supply current or voltage for the transmitter.
What do I have to pay attention to when buying??
The measuring system consists of two components: the transmitter and the thermocouple.
For the complete system, please check that the measurement accuracy, tolerance and response time of the entire measurement system match your specifications.
Furthermore, you should check which signal you need for further processing: 0 to 10 V or 4 to 20 mA.
For the thermocouple, you can make sure that all operating conditions are met and that you order the correct connection or accessories to allow the probe to be used in your process. You will find exact details in each case in the corresponding types and in the associated data sheets. There you will also find detailed installation instructions.
Due to its slim design and standardized dimensions, the Hat rail transmitter fits into your control cabinet. If you require a different type, e.g. in the housing, please contact us.
What are the different types?
Currently we offer active cable thermocouples and screw-in thermocouples.
Cable thermocouple active
Screw-in thermocouple active