Our screw-in probes with connection head can be used in process measurement technology in a temperature range up to 200 °C, 400 °C or 600 °C. They are installed directly in contact with the medium using the G1/2 “ process connection. We offer our screw-in probes with exchangeable measuring insert and according to DIN 43772 in different types.

In this guide, we have compiled information on what you need to consider when selecting, purchasing, installing and operating your screw-in probe.

• What is a screw-in probe with head?
• What different types of screw-in probes with head are there?
• What do I need to look out for when selecting the right screw-in probe with head?
• Replacing a defective probe
• Frequently asked questions about Screw-in probes

What is a screw-in probe with head?

Screw-in probes with connection head are used in process measurement technology. They can be screwed in for temperature measurement in contact with the medium or using an immersion sleeve with an internal thread. There they measure the temperature in gaseous or liquid media. Temperatures of up to +600°C can be measured in pipes, containers or systems. We offer a suitable immersion sleeve, connection cables and thermal conduction paste as accessories. The Screw-in probes can be individually adapted to your application.

Please consider the following points when making your selection

• What is the measuring range, i.e. in which temperature range should the measurement take place?
• What is the ambient temperature? (The heads, housings or connection cables, like the sensors used, also have a temperature range in which they may be used).
• What other ambient conditions prevail (humidity, steam, pressure, vibration?)
• In which medium should measurements be taken?
• How should the temperature probe be installed in the process, i.e. which process connection is required?
• How much space do you have for installing the probe? 

What different types of screw-in probes with head are there?

We offer screw-in probes that are designed in accordance with DIN 43772

• B-Head to DIN 43772 Form 8 without necktube
• Screw-in probe with B-Head - OH 400 °C
• Screw-in probe with B-Head - OH 600 °C

• B-head to DIN 43772 Form 2G with protection tube and neck tube for screwing in
• Screw-in probe with B-Head - HL 600 °C

• B-head to DIN 43772 for screwing into thermowells
• Screw-in probe with B-Head - AH 600 °C

• J-head to DIN 43772 Form 8 without neck tube
• Screw-in probe with J-Head - OH 200 °C
• Screw-in probe with J-Head - OH 400 °C

• J-head to DIN 43772 Form 2G with protection tube and neck tube for screwing in
• Screw-in probe with J-Head - HL 200 °C
• Screw-in probe with J-Head - HL 400 °C
• Screw-in probe with J-Head - HL 600 °C

With these probes, you can determine which mounting length you require and thus determine the immersion depth for these probes. We offer the following lengths (in mm):
50, 100, 150, 200, 250, 300, 400 and 500.

When measuring temperatures in solids or when the probe is mounted in an immersion sleeve, the air surrounding the probe slows down the heat conduction from the medium to the probe. This also slows down the temperature measurement and, in extreme cases, leads to incorrect temperature readings. Therefore, please ensure that the temperature probe is thermally coupled to your measuring medium in the best possible way.

You can choose from the following sensors for all Screw-in probes, depending on the connection head and measuring range:

• Pt100 sensors: Pt100 class A, Pt100 class B, Pt100 1/3 class B, Pt100 1/10 class B
• Pt1000 sensors: Pt1000 class A, Pt1000 class B
• Pt500 sensor: Pt500 class B
• Ni1000
• NTC: 5kOhm, 10kOhm, 20kOhm
• KTY: KTY81-110, KTY81-210
• LM235Z

Other sensors are available on request.

 What do I need to consider when selecting the right Screw-in probe with head?

The right choice of temperature probe depends on your measuring task and the associated requirements for the temperature probe. We often hear questions such as:

• Is the probe also compatible?
• Which sensor type should I choose?
• Can I change my temperature probe?
• Is this the right sensor?
• Which cable do I need or can I replace the cable?

Answering the following questions can help you make the right choice:

1. What is the right sensor?
   In our online store you will find the following sensors for Screw-in probes: Pt100 class A, Pt100 class B, Pt100 1/3 class B, Pt100 1/10 class B, Pt1000 class A, Pt1000 class B, Pt500 class B
   Please pay attention if and if yes which kind of sensor your measuring device / measuring point specifies and please check exactly if the characteristic curve of the sensor fits to the characteristic curve which is stored in your measuring device. If necessary, you will find this information in the operating instructions. The characteristic curves of our sensors can be found here in the overview or also in the operating instructions, which you can download for each sensor type.

2. Does the sensor fit to your measuring range?
   In the operating instructions you will also find the measuring ranges in which the sensor may be used. Please note that the cables, connectors or housings also have a temperature range in which they may be used.

3. What is the correct connection type for your screw-in temperature probe?
   You can order the Pt sensors from us as two-, three- or four-wire versions. Please check at your measuring device / at your measuring point whether you need a three-wire or a four-wire version. The distance between the measuring point and the measuring device should also play a role in your considerations.

   Two-wire circuits
   In two-wire circuits, the intrinsic resistance of the connecting lead adds to the resistance value of the measuring resistor (thermistor or Pt) and thus falsifies the measurement result. If the resistance value of the measuring resistor is large compared to the intrinsic resistance of the connecting lead, this intrinsic resistance can be neglected. However, for measuring resistors with a lower resistance value (e.g. PT100), the intrinsic lead resistance can significantly reduce the measuring accuracy. For this reason, we recommend the two-wire technique in conjunction with low-resistance measuring resistors only if you can use comparatively short connecting leads, i.e. if you only have to cover short distances between the measuring point and the measuring instrument.

   Three-wire circuits
   For applications that require very accurate temperature measurement, we recommend that you use a three-wire or even four-wire circuit. In the three-wire circuit, the lead resistance of each of the three connected cables is determined using the third connected cable (all connecting wires must be exactly the same length) and then subtracted from the total measured resistance (measurement resistance + lead resistance), so that effectively only the resistance value of the measurement resistance is used for temperature determination. This subtraction can be performed automatically in the measurement electronics, for example.

   Four-wire circuits
   The safest and most accurate measurement is achieved using a four-wire circuit. Here, an additional cable is connected on each side of the measuring resistor. Two cables are used for the voltage supply, the other two are used to determine the line resistance (if necessary also asymmetrically, i.e. also with connecting wires of different lengths) and to subtract it from the measured resistance value. This subtraction can be carried out automatically in the measurement electronics, for example.

4. How do you ensure the correct mechanical connection of the temperature probe to the process?
   Correct mechanical connection of the temperature probe to the process ensures efficient, error-free and trouble-free measurement.

   Thread size / process connection
   For Screw-in probes, please make sure to select the correct thread size and use the thread according to the operating instructions.

   Mounting length
   For temperature sensors with metric screw-in threads (as G1/2", G1/4" and G3/8") you can choose the mounting length. Please measure in advance which mounting length you need. Each probe requires a minimum immersion depth in order to accept and correctly measure the temperature of the medium to be measured. As a rule of thumb, the following advice can serve you: optimally, the immersion depth should correspond to 10 times the thermowell diameter, but at least a 5-fold value should be used.
   More detailed information on installation and immersion depths can be found in the operating instructions, which can be downloaded for each probe.

   Environmental influences
   Please also pay attention to whether you have certain requirements at the measuring point or in your process regarding temperature, pressure, IP protection, steam or similar and compare your specification with our data sheets. If you have any questions or are unsure, please feel free to contact us.

5. What do I have to consider when mounting the temperature probe?
   Please check whether you need accessories for the correct mounting of your Screw-in probe. If necessary, thermal paste can improve the conductivity and thus the response time. Maybe you also need a suitable immersion sleeve?

6. Which accessories do you need for your temperature probe?
   Please check the delivery details for each temperature probe to see what is included in the scope of delivery and consider whether you need accessories when placing your order.
   We offer the following accessories:

• Cables
• Immersion sleeves