What are the voltage requirements for the Digital Inputs on the 5500sc Silica and Phosphate analyser?
Specifications for the TTL and Open Collector settings for the Digital Inputs on 5500sc
In the TTL configuration. a 3-30 VDC signal is applied to the terminals and this causes the analyser to skip the sample stream correlating to that input.
If the jumpers are moved to change the inputs to be Open Collector inputs, the power is supplied by the analyser and then you would only need a dry contact closure to cause the instrument to skip that stream.