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When using pressure sensors, the output signals 0 ? 20 mA, 4 ? 20 mA and DC 0 ? 10 V are frequently chosen in order for the sensor signals to be evaluated and additional processed. Because of this, the signal output of the pressure sensor is normally linked to a corresponding input card in the PLC.
In this context it can often be confusing, because the day-to-day usage of 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 pressure gauge octa , which represents the ?passive part?. Sometimes the active section of the interconnection is also referred to as an electrical source/voltage source and the passive part is known as a ?current sink?. In order that an electrical circuit can function, current must flow in a circuit ? even when an instrument is normally known as a load, 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 pressure gauge and current sink, therefore the power source operates actively (= sending out current) and the current sink passively (= current flows through it) . Therefore, เกจวัดแรงดัน of two current sources or two current sinks won’t operate normally. This situation 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 PLC operate?
As a rule of thumb, you can understand that 2-wire sensors usually work passively and thus 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 a dynamic or passive 0/4 ? 20 mA signal output. Hence, it is imperative to check the datasheets for the sensor and PLC input card used.