NTC Probes

An NTC can be a good choice when you need to measure within a relatively small temperature range below 200 °C – for example, when measuring the room temperature, the temperature in a refrigerator or in a boiler. With temperatures above 200 °C or a wide required range, we recommend a Pt1000 instead.

Due to the extremely high resolution, NTCs can be very accurate within a limited range. However, since their curve is exponential, this is only the case in a fairly small temperature range. In addition, unlike Pt100, Pt1000 and thermocouples, NTCs are not standardised. Therefore, there is a confusing variety of NTC sensing elements.

An interesting advantage of the NTC over other resistance thermometers comes into play with long cables: the comparatively high reference resistance of usually well over 1,000 ohms ensures that the cable resistance is virtually insignificant even with long cable lengths.

To select an NTC, you must either know or define two important values:

First, the nominal value. This is the resistance at a reference temperature. For NTC, the resistance at 25 °C is usually specified here. An NTC with the designation “3k3” or “3.3k” has a resistance of 3,300 ohms at this reference temperature.

Another important factor is the beta value. It indicates the temperature coefficient and thus the course of the characteristic curve.

If you are unsure about these values, get in touch with our experts – we are happy to help you find the right NTC.

Regarding the response time of a sensor, the following rule of thumb applies: If you double the diameter, you quadruple the response time. So choose the diameter wisely!

As with all temperature sensors, the immersion length should be at least 5x the diameter of the sensor to avoid thermal bridges.