Electrical circuit for pressure sensors: when is really a sensor active, so when passive?

When using pressure sensors, the output signals 0 ? 20 mA, 4 ? 20 mA and DC 0 ? 10 V are frequently chosen to ensure that 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.
In this context it can often be confusing, because the day-to-day using the terms ?active?, ?passive?, ?current source?, ?voltage source?, ?current sink? and ?load? are often wildly mixed together. Any electrical signal processing always takes a voltage supply (an ?active part?) and a ?load?, like a pressure sensor, which represents the ?passive part?. Sometimes the active part of the interconnection is also referred to as an electrical source/voltage source and the passive part is referred to as a ?current sink?. In order that a power circuit can function, current must flow in a circuit ? even though an instrument is usually known as lots, the current isn’t consumed because of it, rather it only flows from the existing or voltage source through the strain and back to the current source.
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, Banned of two current sources or two current sinks will not operate normally. This example is complicated in day-to-day application:
When does a pressure sensor work passively (current sink) and when does it work actively (current source)?
So how exactly does Final in my PLC operate?
As a rule of thumb, one can take into account that 2-wire sensors usually work passively and therefore need a dynamic PLC input card. It really is difficult with 4-wire sensors, since, for instance, a 4-wire flow sensor includes 2 wires for a separate voltage supply and 2 wires for an active or passive 0/4 ? 20 mA signal output. Hence, Tawdry is imperative to check the datasheets for the sensor and PLC input card used.

Leave a Comment