SmartPlate EV Installation, Operation and Maintenance Manual
CHAPTER 3
– FUNCTIONAL DESCRIPTION
OMM-0147_C
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The Controller continuously monitors the
unit’s outlet temperature via a thermocouple located in
the outlet port. The Controller also receives a feed-forward signal from the Flow Meter shown in
the DHW inlet piping. The Flow Meter monitors flow changes through the unit and provides a
feed-forward signal to the Controller proportional to the change in flow. The Flow Meter provides
an instantaneous feed-forward response for loads ranging from 3 GPM to the maximum Water
Heater flow.
The Controller provides a 4 to 20 mA output signal to the 3-Way Control Valve Actuator. This
signal proportionally modulates the Control Valve position from fully closed (4 mA) to fully open
(20 mA). The control signal varies as necessary to maintain the setpoint temperature
programmed into the Controller. Under normal conditions,
the unit’s outlet temperature is
maintained within ±4°F of the desired setpoint based on a load change of 50% or less.
3.4 OVER-TEMPERATURE CONTROL AND SAFETY FEATURES
The Control Box contains an Over-Temperature switch that continuously monitors and displays
the
unit’s outlet water temperature from input received from the thermocouple installed in the hot
water outlet port. Normally, the Over-Temperature switch is set 20°F above the
unit’s setpoint
temperature. If the programmed over-temperature limit is exceeded, the Over-Temperature
switch is activated. This in turn sounds an audible alarm and disconnects power from the 3-Way
Control Valve Actuator, moving the Control Valve to the full-bypass position (B). It should be
noted that the Over-Temperature switch has a slightly slower response to temperature changes
than the Temperature Controller. Therefore, slightly different temperature readings may appear
momentarily in their respective displays, particularly during system start-up.
The Control Valve Actuator also incorporates a “Fail-Safe” feature, which automatically closes
the valve if there is a loss of the 4 to 20 mA control signal or loss of input power. The 24 VAC
power supply transformer has an integral 3 amp fuse on the harness to protect the 3-Way
Control Valve electronics.
