Automatic Purging Mode / Holding Torque - Emotron EMX Serie Manuel D'instructions

1.3.1

Automatic purging mode / holding torque

When the control signal is low, <1.5 V at 0–10 V, the drive system switches to
purging mode. In purging mode the motor shaft turns two revolutions every 10
minutes, which is equivalent to around 30 degrees of rotation by the heat
exchanger rotor. This slow rotation does not provide any significant heat
transfer, but simply serves to keep the heat exchanger rotor clean.
Most of the time the heat exchanger rotor seals keep the rotor stationary, but if
the rotor seals are not touching the rotor and the air flow is not perpendicular to
the rotor, the air flow may cause the rotor to rotate. To prevent unintentional
heat recovery in this situation the motor is automatically used to provide a
holding torque to keep the rotor stationary.
The first time the drive system goes into purging mode after the power is
switched on this holding torque is not activated, since many heat exchanger
rotors do not require an active holding torque to keep them stationary. A rotor
that does require a holding torque will then begin to turn slowly. The drive
system immediately brakes this motion, reducing the speed to zero, and then
applies a constant holding torque to keep the rotor stationary. The drive system
has now learned which rotors require a holding torque, and which do not. The
holding torque is at least 50% higher than the torque required for operation just
before stand still.
If a holding torque has been applied and you grasp the drive belt and try to turn
the heat exchanger rotor by hand, the torque will progressively increase.
The holding torque is generated by passing a current through one of the motor
phases. The higher the torque that is required, the higher the current. This
current produces a noise that gets louder as the current increases. Integrated in
the control unit are three motor protection breakers, one for each motor phase.
The motor protection also protects the motor when the holding torque is
activated.
6 Description Emotron AB 01-3333-01r3