Questions about the input module! !
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There is an existing digital input module with 16 channels and 24VDC supply. How can it be used to input passive contact signals as well as 220VAC digital input signals?
Passive contact signals require a 24V DC power supply; the negative terminal is connected to the COM of the 24VDC digital input module, while the positive terminal supplies power to each passive contact, from where it is then sent back to the 24VDC digital input module. The 220VAC digital input signal must first drive a 220V relay, and then be used via passive contacts! (This is safer, but other methods can also be used.) Last edited by liuei on 2009-2-25 21:05]
If the operations are frequent and high reliability is required, relays cannot be used for isolation; instead, dedicated optoelectronic conversion isolation modules must be employed!