Active temperature measurement is as diverse as passive temperature measurement. That is why there are also many different types of active probes.
In this guide, we have compiled information on the difference between active and passive temperature probes, the advantages of using an active probe and what you need to bear in mind when selecting, purchasing, installing and operating your active temperature probe.
What is an active temperature probe?
An active temperature probe is an electronic assembly consisting of a temperature probe and a transmitter or measuring transducer. Depending on the design, the probe and transmitter can be permanently connected or the probe can be flexibly connected to the transmitter. In this case, only the probe or transmitter can be replaced in the event of a defect.
The probe measures the temperature and transmits it as an electrical signal to the display, the control unit or the heating system.
Unlike passive temperature probes or thermocouples, it does not output the thermoelectric voltage or resistance value.
Instead, the transmitter ensures that a standardized output signal is given as a voltage in mA or as a current in V. The temperature sensor can now be connected to the display or the control unit. This means that the temperature probe can now be used on many standard instruments.
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.
There is also a disadvantage: unlike the passive probe, which does not require an external power supply, a supply voltage or current must be used to convert the signal.
For the individual components of the temperature probe, the same questions arise as for the passive probe, so that the probe is well suited to the measuring task:
- In which medium shall be measured?
- How is the measurement to be performed (penetration measurement, surface measurement, etc.)?
- 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?
We currently offer the types cable probe with stainless steel sleeve and Screw-in probe with G1/2", G3/8", G1/4", M4, M6 and M8 thread as active temperature probes. If you need another type, e.g. room temperature probe, outdoor probe, Radiation probe or other probes in plastic housing or duct probe, head probe or similar, please feel free to contact us - we will be happy to check what we can offer you. This also applies if you require a different transmitter shape, e.g. in the housing.
As the measuring system now consists of two components the accuracy, response time and tolerance of the complete 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 temperature probe work?
An active temperature probe detects the temperature as resistance (resistance-based temperature probes) or as thermoelectric voltage (thermocouples), depending on the sensor. This signal is converted by a temperature transmitter into a standardized output signal: either in current - in which case the output is in amperes (mA) or in voltage - in which case the output is in volts (V). Which output signal is selected depends in turn 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 temperature probes are somewhat more expensive than passive temperature probes. 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 also 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 needed in order to process the measurement data. This is provided by active probes.
For which applications do I need an active temperature probe?
Typically, active probes are used in heating technology, building services engineering, air conditioning technology or plant engineering. Here, you measure the temperature of the 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 sensor if you need a signal between 4 to 20 mA or in 0 to 10 V for further processing, if you want to bridge longer distances between measuring point and evaluation unit or if you want to ensure and permanently monitor that a measuring signal arrives.
You have to take care 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 temperature probe or 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 temperature probe, 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.
