The output relay is actuated when the control voltage is switched on
and the resistance of the PTC thermistor temperature sensor is
low. The auxiliary contacts operate. On reaching the nominal actuation temperature (NAT), the
sensor resistance becomes high and causes the output relay to drop out. The defect is
indicated by an LED. As soon as the sensors have cooled enough so that the respective smaller
resistance is reached the EMT6-(K) switches automatically on again. With the EMT6-(K)DB(K)
the automatic re-switch on can be defeated by switching the device to “Hand”. The unit is
reset using the reset button.
The EMT6-K(DB) and EMT6-DBK are fitted with a short-circuit in sensor circuit
monitor. Should the resistance in the sensor circuit fall below 20 Ohm it trips. The EMT6-DBK
also has a zero voltage safe, re-switch on lock-out and stores the fault by a loss of voltage.
Switching on again is possible only after the fault has been rectified and the control
voltage is present again.
Since all the units use the closed-circuit principle, they also respond to
a broken wire in the sensor circuit.
The thermistor machine protection relays EMT6… are accredited for protection of
EEx e motors to ATEX-Guideline 94/9 EG by the German Physical/Technical Bureaux. For
protection of EEx e motors the ATEX Guidelines require short-circuit monitoring in the
sensor circuit. Because of their integrated short-circuit monitoring the EMT6-K(DB) and
EMT6-DBK are especially suitable for this application.
