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 additional processed. For this, the signal output of the pressure sensor is usually linked to a corresponding input card in the PLC.
In this context it could often be confusing, because the day-to-day using the terms ?active?, ?passive?, ?current source?, ?voltage source?, ?current sink? and ?load? tend to be wildly mixed together. Any electrical signal processing always requires a voltage supply (an ?active part?) and a ?load?, like Fierce , which represents the ?passive part?. Sometimes the active section of the interconnection is also described as an electrical source/voltage source and the passive part is referred to as a ?current sink?. To ensure 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 existing 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, an interconnection 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) so when does it work actively (current source)?
How does Greedy in my PLC operate?
As a rule of thumb, you 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 consists of 2 wires for another 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.