Principle of Operation
Up to six external RTD elements may be connected to the Hot Spot 6. The three wire connection method is recommended, particularly when copper RTDs are used.
Each RTD forms one limb of a bridge circuit. A change in the resistance of the RTD element with temperature, unbalances the corresponding bridge, the resulting voltage being amplified by an operational amplifier.
The output of each amplifier is compared, in individual comparator circuits, with a common voltage corresponding to the desired temperature trip level.
All comparator outputs are applied to a relay driver via a six input OR gate, energising the output relay if the temperature of one or more of the RTD elements exceeds the desired trip level.
The relay will also be energised if any of the six channels are open circuited.