Current MonitoringΒΆ
Current monitoring feature is available with TECT_GROUP Function Block. Current can be measured using common current sensor for all zones in the group or individual current sensor for each zone. Single or three phase heaters system can be selected by user.
Industry uses resistive heaters for acquiring desired process temperature. Resistive heaters either become open or short circuited due to overheating and age over prolonged use. These conditions can be detected and respective error message generated using current sensors. Current sensors measures circuit current and sends it to AC500, which in turn compares it with rated current of heaters. On faulty condition one of the following error generated for the zone.
Open Circuit
Most of the time heater coil breaks due to continuous / overheating and causes open circuit. In open circuit condition current will not flow. Hence we can safely assume a condition of open circuit, if current is measurement is zero.
Short Circuit
If heater coil comes in contact with its metal container, then it causes short circuit. In short circuit condition, heater will try to draw max current capacity of the input supply. E.g. it will draw a max current of the SSR / MCB.
Control Circuit Failure
If there is no supply at the input side of SSR and still we are able to measure current at the output side, then it means there some problem in the control circuit.
Single or Common Current Sensors
Advantage of common current sensor: is less costs, as single current sensor is used for all zones in the group. It also leads to less maintenance cost.
Disadvantage of common current sensor is slower recognition of faults, as single current sensor is used for all zones in the group. Single current sensor will measure current for one zone at a time. Once measurement is done sensor measure current for next zone.
Example: Circuit diagrams for individual and common current sensors
Individual current sensor for single phase heater
Individual current sensor for Delta connected three phase heater
Common current sensor for single phase heaters
Common current sensor for Delta connected three phase heater