The temperature probes that could be used for this purpose are as versatile as your applications. In measurement and control technology and in the control of processes and systems, correctly recorded temperatures are crucial for the trouble-free operation of the systems. In heating systems, temperature probes ensure the correct recording of the outside or room temperature or the correct temperature in buffer storage tanks or on heat pumps.
In this guide, we have compiled information on what you should pay attention to when selecting, purchasing, installing and operating your bayonet probe.
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?
- In which ambient temperature will be worked? (The heads, housings or connecting cables, just like the sensors used, also have a temperature range in which they may be used).
- Which other environmental conditions prevail (humidity, steam, pressure, vibration)?
- In which medium shall be measured?
- How should the temperature probe be attached to the process?
- How much space do you have for the installation of the probe?
What are the different types of bayonet temperature probes?
We offer bayonet probes with three different tips. For bayonet probes, you can choose the diameter of the bayonet probe tip (6 mm or 8 mm) and the diameter of the bayonet cap (12 mm or 14 mm).
Our three types are:
You can choose from the following sensors for all bayonet probes:
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
Other sensors are available on request.
What should I pay attention to when selecting the right bayonet temperature probe?
The right choice of temperature probe depends on your measuring task and the associated requirements for the temperature probe. We often hear questions like:
- Is the probe compatible?
- Which sensor type should I choose?
- Can I change my temperature probe?
- Is this the right sensor?
- Which cable do I need or even can I replace the cable?
Answering the following questions may help you in your selection:
What is the right sensor?
In our online store you can find the following sensors for contact 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.
Does the sensor fit 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.
What is the correct connection type for your bayonet 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.
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.
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.
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.
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.
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, feel free to contact us.
What do I have to consider when mounting the temperature probe?
Please check if 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?
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:
Replacing a defective probe
When replacing a defective temperature probe, please pay close attention to which temperature sensor you require. Sensors such as PT100, PT1000, KTY, NTC or thermocouples are not compatible with each other. Therefore, please check the technical data of the respective system which sensor type is required. If the required information is not apparent in the operating instructions of the measuring instrument / device, the manufacturer of the machine or system should be contacted in case of doubt.
Once you have found the correct sensor, please also test the mechanical connection. The temperature can only be measured correctly if the temperature probe can be attached to the mounting location in accordance with the regulations. Otherwise, machines and equipment can easily malfunction.
Please also make sure that you order thermal paste and mounting accessories such as compression fittings, cutting ring screw fittings or bayonet nipples if these also need to be replaced.
Frequently asked questions about temperature probes
The temperature probe shows strange values? The temperature probe does not show any values? This behavior may indicate that your temperature probe is defective or that it has not been connected correctly.
To find out if there is a defect, you can simply measure the resistance value of resistance-based temperature probes and compare it with the specification on the probe itself or in the user manual. You can use a standard multimeter to do this.
If you are using a thermocouple instead of a resistance-based temperature probe, the situation is somewhat different. Here you need a multimeter with an appropriate connector for thermocouples, because thermocouples do not have a resistance signal, but a voltage signal.
Alternatively, you can test on a trial basis whether a replacement will remedy the situation.
How do I connect the temperature probe correctly?
When connecting your temperature probe, please make sure that you follow our wiring diagrams. You will find the wiring diagrams in the operating instructions for your temperature probe.