Digital probes and analog probes – where are they used?

The similarities between digital and analog probes can make it difficult for the user to choose the right sensor. Find out which probe is right for you here.

Digital probes and analog probes (such as linear potentiometers) are sensors used for tactile measurement. That means that they take measurements with direct contact to the object being measured. To do this, the sensors are equipped with a ball tip and a return spring. In the case of particularly sensitive surfaces or measurements in the µm range, digital probes are also equipped with a pneumatic pin guide instead of a spring. Unlike optical measuring systems, digital and analog probes take measurements without regard to the colour and transparency of the measured object or ambient light.

The basic difference between the two measuring systems, however, lies in their measurement principle and the resulting respective strengths.

Digital probes from the GMR series are based on the principle of optical linear scales. Inside them, there is a scale connected to the probe, which moves when the probe is retracted or extended. This change in position is compared with a reference scale and output as a precise RS-422 signal. Digital probes offer a high level of accuracy and high resolution. They also have a very long service life thanks to the wear-free measurement technology. This type of probe is ideal for dynamic applications or for measurements that require extreme accuracy due to its high number of cycles.

Analog probes such as linear potentiometers work according to the voltage divider principle. They feature a sliding contact (wiper) connected to the piston rod, which travels over a resistance track. The resistance varies according to the position of the wiper, which makes it possible to determine the exact position of the wiper and thus of the piston rod. Linear potentiometers from the LRW2 series are cost-efficient linear sensors and provide a good alternative to digital sensors in series production. In contrast to digital probes, linear potentiometers can easily be used for larger measuring ranges of up to 150 mm. They also feature a wide operating temperature range of -30 to +100 °C. One further strength of the measuring principle is that linear potentiometers can be used as passive components according to EN 60079-11. They are therefore also suitable for certain ATEX areas.

These advantages are why linear potentiometers are used in many areas of industry and research. One typical area of application is in the field of resistance welding, where many other sensor systems are negatively affected by the high temperatures and strong electrical currents.

A third alternative in the field of tactile measurement is offered by LVDTs. The sensors rely on the inductive measuring principle and are ideal for extreme applications such as induction melting furnaces due to their high accuracy and durability.