Sinking vs Sourcing Inputs and Outputs Question (with Answer & Explanation)
Question – Sinking vs Sourcing IO:
Q1 - Which figure shows a SOURCING digital input card? And for that diagram, what would the voltage read on the Ch1 input terminal if the input switch was open? (assuming negative lead is on the 24v common).
Q2 - Whis figure shows a SINKING digital output card? And for that diagram, what would the voltage be at the Ch1 output terminal if the output channel was active (assume the negative lead is on the 24v common).
Thoughts? Experiences? Comments/Notes?
Answers / Explanation:
Answer for Q1: Figure 1 is a SOURCING input card. Voltage on Ch1 input terminal (in ref to PS common) would be approximately source voltage (24vdc) if the sensor (switch) was open.
Answer for Q2: Figure 3 is a SINKING output card. Voltage on Ch1 output terminal (in ref to PS common) would be approximately 0vdc if the output was active (ON state).
This topic causes much confusion and there are many variables that may impact the voltage readings.
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Mike Glass
Mike Glass is an ISA Certified Automation Professional (CAP) and a Master Certified Control System Technician (CCST III). Mike has 38 years of experience in the I&C industry performing a mix of startups, field service and troubleshooting, controls integration and programming, tuning & optimization services, and general I&C consulting, as well as providing technical training and a variety of skills-related solutions to customers across North America.
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