What is an immersion probe with head?
Immersion probes with connection head are used in process measurement technology. They can be plugged in for temperature measurement in contact with the medium or coupled indirectly to the process using immersion sleeves. There they measure the temperature in gaseous or liquid media. Temperatures up to +600°C can be measured in pipelines, vessels or plants. We offer brass or stainless steel immersion sleeves as accessories. The immersion temperature sensors 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?
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 installed in the process, i.e. which process connection is required?
How much space do you have for the installation of the probe?
What are the different types of immersion probes with heads?
We offer immersion probes with four different measuring ranges and connection heads.
With these probes, you can determine which mounting length you need and thus the immersion depth for these probes. We offer the following lengths (in mm):
50, 100, 150, 200, 250, 300, 400 and 500.
When measuring temperature 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 immersion probes, depending on the connection head:
- 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
- NTC: 5kOhm, 10kOhm, 20kOhm
- KTY: KTY81-110, KTY81-210
Other sensors may be possible on request.
What should I pay attention to when selecting the right immersion 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 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 immersion 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 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.
What is the correct connection type for your immersion probe with head? 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 inherent resistance of the connecting cable 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 by 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 performed 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.
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, feel free to contact us.
What do I have to consider when mounting the temperature probe? Due to the heat dissipation to the environment, measuring errors can occur. To keep these as small as possible, we recommend to immerse the protection sleeve of your temperature probe as deep as possible into the medium to be measured during installation. The optimum installation depth should be 10-15 times the Ø of the protection sleeve or, when using an immersion sleeve, the Ø of the immersion sleeve. When installing in pipelines whose Ø does not have a sufficiently deep installation depth, you should install the probe either at an angle or in a pipe elbow. Make sure that there is sufficient space for the probe to be removed.
Installation by means of compression fitting: Please tighten the union nut of the compression fitting by hand as far as it will go (clearly noticeable). With a wrench matching the wrench size, please make a 1/4 turn on compression fittings with PTFE thrust collar. These compression fittings can be used several times in this way. In the case of compression fittings with stainless steel cutting ring, the compression fitting connects to the protection tube. This connection is pressure resistant up to 40 bar. However, the compression fitting can only be used once. It must also be tightened more firmly. Please tighten it with 1 3/4 turns.
Mounting by means of mounting flange: Please make sure that the Ø of the mounting flange matches the Ø of the protection sleeve.
Mounting by using an immersion sleeve: Please note that the Ø and the length of the immersion sleeve must be selected to match the installation situation so that the minimum immersion depth can be achieved. Since the probe is not inserted directly into the medium, but via the immersion sleeve, the response times are somewhat slower. The probe should be selected in such a way that the protection sleeve touches the bottom of the immersion sleeve and that the air cushion around the protection sleeve is as small as possible. The use of thermal paste can improve the response times.
Please lay the cable with reserve loop and in such a way that no water can penetrate into the sensor head. This will allow you to extend the probe without disconnecting the electrical connection.
Which accessories do you need for your temperature probe?
Please check the delivery details for each temperature probe to see what is included and consider whether you need any accessories when you place your order.
We offer the following accessories:
Replacement of a defective probe
When replacing a defective temperature probe, please pay close attention to which temperature sensor you need. Sensors like 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 to order thermal paste and mounting accessories such as compression fittings, cutting ring screw fittings or bayonet nipples in case these also need to be replaced.
Frequently asked questions about temperature sensors
How can I tell that my temperature probe is defective?
The temperature probe shows strange values? The temperature probe does not show any values? This behavior can be a sign 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.