This module monitors the incoming power to the equipment shelter by measuring the supply voltage and the supply current. This allows the system to monitor is power consumption to determine if experimental setups are drawing too much power.
The supply current to the enclosure is measured using a Hall-effect current sensor ACS-712. The rated capacity of the +24V supply feeding the enclosure is a maximum of 5A. A 20A version of this sensor is available and provides a level of overhead if the supply ever provides more than its rated 5A. This sensor uses a +5V supply and the output range is 0.5V (-20A input) to +4.5V (+20A input). The output voltage in the range 0A to +20V is +2.5V to +3.0V. Scale and offset adjustment is carried out in the software.
The ADC can only tolerate a maximum input of +3.6V (VDD + 0.3V) and this corresponds to just over +10A of supply current. As a 100% current overload is not likely given that the +24V supply is regulated and protected, but to account for this unlikely possibility, the sensor is connector so that an increase in current will result a reduction of output voltage towards 0V output, rather than +5V output. it has been decided that a voltage divider on the output of the current sensor is not required.
The power monitor has a set of power input terminals to accept the incoming power cable; and a corresponding set of output terminals where the power is connected to the DIN rail input terminals. It also has a flying cable from the monitor box to the DIN rails terminals that brings power to the monitor and accepts the current and voltage sensor readings from the power monitor box.