Voltage generating sensors

Some sensors have outputs that generate different voltage levels depending on whether they are ON or OFF. The controller can differentiate between these two levels. Its input circuits would be described as "voltage sensing".

Typical voltage generating sensors are:

• Quadrature encoders and digital potentiometers (frequently available with a choice of output types)
• Custom made or highly specialized sensor circuits from companies with limited exposure to industrial markets (and hence a lack of appreciation for how "things are normally done").

In general, it can be risky to try and connect a voltage generating sensor to a controller designed for NPN, PNP or dry contacts. The controller will generate its own voltage, which if applied to a voltage generating sensor could damage the sensor, the controller or both.

For example, a typical voltage generating sensor will use "TTL" levels. That means its internal circuits run off 5V and its normal output voltages will be between 0.2V and 3.5V. If that circuit was connected to a controller that supplies 24V at its input pins, it would probably not survive.

The other way around, connecting a sensor with NPN, PNP or dry contact outputs into a voltage sensing controller, is unlikely to damage anything but will not work. If it does appear to work, beware! it may not be reliable.

It is quite uncommon to see a general purpose programmable controller that is specified to work with voltage generating sensors. That means if for some reason you are stuck with a voltage generating sensor (maybe something that has been custom made for you), you may have a challenge to find a compatible controller. Also, you will have to make a detailed match between the sensor specification and the controller. One solution could be to use a controller with a "programmable comparator" input or use an analog input. Or, if you are having a custom SPLat made, we can accommodate virtually anything.