Hello! How can I connect an analog sensor to an analog PLC module? The sensor outputs a standard 4-20mA signal, typically featuring two outputs: +4-20mA and -4-20mA. I plan to connect the +4-20mA output to the I+ terminal. However, I’m unsure where to connect the corresponding output to the PLC communication port. Any guidance would be appreciated. Thank you!
The 0V line is essential for proper operation of the 4-20mA signal, necessitating a shared common 0V between your analog input module and the sensor. If your sensor operates on a different power supply, it's crucial to link the two 0V connections together. However, if this connection is not feasible or could lead to common grounding issues, it's advisable to employ a 4-20mA signal isolator. Without such an isolator, the 0V from the sensor may inadvertently connect to the sensor’s power supply and a common COM, while the 4-20mA signal will be directed to the I+ terminal, which should be linked to the V+ terminal for optimal functionality.
1. A 4-20mA output consists of both a positive (+) and a negative (-) terminal. In the case of active outputs, which are powered internally by the field device, the positive terminal connects to the AII and AIV terminals, while the negative connects to the COM terminal. According to the installation guide, a jumper is required between the V terminal and the I terminal for proper current input wiring. 2. The provided wiring diagram is based on the assumption of an active, powered 4-20mA signal. If the field device responsible for generating the 4-20mA signal is loop-powered, then the wiring must include a DC power supply. For connections involving a loop-powered field device, the following setup is necessary: the power supply's positive (+) terminal connects to the field device's positive (+) terminal; the field device's negative (-) terminal connects to both AII and AIV; and the AI COM terminal connects to the power supply's negative (-) terminal. 3. It is important to note that there is no such thing as a "negative 4-20mA" signal. For instance, measuring vacuum pressure from atmospheric conditions down to -1.0 Bar encompasses a spectrum of negative values; however, the signal format remains a conventional 4-20mA representation. Although the 4-20mA can denote a range or scale of negative engineering unit values, it does not encompass a (-)4-20mA signal.
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