{"id":878,"date":"2012-08-01T07:40:16","date_gmt":"2012-08-01T05:40:16","guid":{"rendered":"http:\/\/wika-blog-live.mcon.net\/?p=878"},"modified":"2021-12-02T09:00:23","modified_gmt":"2021-12-02T08:00:23","slug":"active-passive-sensor","status":"publish","type":"post","link":"https:\/\/blog.wika.com\/en\/products\/pressure-products\/active-passive-sensor\/","title":{"rendered":"Electrical circuit for pressure sensors: when is a sensor active, and when passive?"},"content":{"rendered":"

When using pressure sensors, the output signals 0 \u2026 20 mA, 4 \u2026 20 mA and DC 0 \u2026 10 V are frequently chosen in order for the sensor signals to be evaluated and further processed. For this, the signal output of the pressure sensor is usually connected to a corresponding input card in the PLC.<\/strong><\/p>\n

In this context it can often be confusing, as the day-to-day usage of the terms “active”, “passive”, “current source”, “voltage source”, “current sink” and “load” are often wildly mixed together. Any electrical signal processing always requires a voltage supply (an “active part”) and a “load”, such as a pressure sensor, which represents the “passive part”. Sometimes the active part of the interconnection is also described as a power source\/voltage source and the passive part is referred to as a “current sink”. In order that an electrical circuit can function, current must flow in a circuit – even when an instrument is usually known as a load, the current is not consumed by it, rather it only flows from the current or voltage source through the load and back to the current source.<\/p>\n

This works only if an “energy gap” exists between current source and current sink, so the power source operates actively (= sending out current) and the current sink passively (= current flows through it) . Therefore, an interconnection of two current sources or two current sinks will not operate normally. This situation is complicated in day-to-day application:<\/p>\n