Monitoring JACE 8000 Power Supply Voltage for Fault Diagnosis
Overview
The JACE 8000 does not provide a built-in register for monitoring its 24 VDC power supply voltage. However, monitoring this value can be extremely useful for diagnosing intermittent issues caused by unstable power. This guide outlines a simple workaround using a spare Analog Input (AI) and a resistor divider network.
Why Monitor Power Supply Voltage?
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Detect voltage drops or fluctuations that may cause controller instability.
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Trend the supply voltage over time for historical analysis.
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Assist in root cause analysis for unexplained site issues.
Solution: Resistor Divider with AI Input
If you have a spare AI input, you can scale the 24 VDC supply down to a safe range (0–10 V) using a resistor bridge. This allows the JACE to read and log the voltage using a history.
Circuit Design
The following resistor network reduces 24 VDC to approximately 10 VDC for the AI input:
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R1: 14 kΩ
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R2: 10 kΩ
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R3 (Protection): 1 kΩ (series with AI input)
Purpose of R3:
Provides current limiting in case of divider failure or accidental short.
