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

When using pressure sensors, the output signals 0 ? 20 mA, 4 ? 20 mA and DC 0 ? 10 V are generally chosen in order for the sensor signals to be evaluated and further processed. Because of 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, as 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 ? ไดอะแฟรม ซีล ?) and a ?load?, such as a pressure sensor, which represents the ?passive part?. Sometimes the active portion 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 a power circuit can function, current must flow in a circuit ? even though an instrument is usually known as a load, the current is not consumed by it, rather it only flows from the existing or voltage source through the load and back to the current source.
This works only if an ?energy gap? exists between current source and current sink, therefore 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. ไดอะแฟรม is complicated in day-to-day application:
When does a pressure sensor work passively (current sink) so when does it work actively (current source)?
So how exactly does the input card in my PLC operate?
Generally of thumb, one can understand that 2-wire sensors usually work passively and thus need an active PLC input card. It really is difficult with 4-wire sensors, since, for example, 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. It is therefore imperative to check the datasheets for the sensor and PLC input card used.