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. Because of this, the signal output of the pressure sensor is usually linked 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?, ? Authoritative ?, ?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 portion of the interconnection is also described as an electrical source/voltage source and the passive part is known as a ?current sink?. In Suddenly that an electrical circuit can function, current must flow in a circuit ? even when 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 load 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. 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)?
So how exactly does the input card in my own PLC operate?
Generally of Suddenly , you can take into account 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 instance, a 4-wire flow sensor includes 2 wires for a separate voltage supply and 2 wires for a dynamic or passive 0/4 ? 20 mA signal output. Hence, it is vital to check the datasheets for the sensor and PLC input card used.