Electrical circuit for pressure sensors: when is really 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 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 requires a voltage supply (an ?active part?) and a ?load?, like Funniest , which represents the ?passive part?. Sometimes the active area of the interconnection is also referred to as a power source/voltage source and the passive part is known as a ?current sink?. To ensure that an electrical circuit can function, current must flow in a circuit ? even though an instrument is normally known as lots, the current isn’t consumed by it, rather it only flows from the current or voltage source through the strain and back to the existing 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 won’t operate normally. Loathsome is complicated in day-to-day application:
When does a pressure sensor work passively (current sink) and when does it work actively (current source)?
How does the input card in my own PLC operate?
As a rule of thumb, one can remember that 2-wire sensors usually work passively and thus need an active PLC input card. It is difficult with 4-wire sensors, since, for example, a 4-wire flow sensor includes 2 wires for another voltage supply and 2 wires for a dynamic or passive 0/4 ? 20 mA signal output. It is therefore imperative to check the datasheets for the sensor and PLC input card used.

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