Built-In motor PTC with Siemens G120 VFD

[Jieve]

Hello all,

I am using a Sinamics G120 CP 240E-2 PN-F control unit to drive a Siemens 1LE10030DA222AB4 3-phase 1hp (0.75kW) motor. The motor has a sticker saying "Umax 30V DC PTC Thermistor". I have connected the 2TP motor terminals 1 & 2 inside the terminal box, which I am assuming are from the PTC, to the Control Unit inputs 14 and 15, labeled T1 Motor and T2 Motor. I configured the setup to use a PTC in the basic commissioning wizard of the drive. I do not get a fault since the resistance is just above the 20 ohms for a short circuit alarm, but the monitored motor temperature is a constant -200C. I have measured the resistance of the motor PTC thermistor and get a measured 75.5 ohms.

Am I doing something incorrectly? Any ideas why I'm not getting the correct resistance/ motor temperature reading?

Thanks for any reply.

 

[Jieve]

I received a response from the Siemens message boards that motor PTC sensors are not used to monitor a range of motor temps due to their non-linear behavior. They are simply used with VFDs to trigger overtemp alarms at 1670 Ohms or something like this. Is this correct?

If so, would a KTY84 would be used to monitor actual temps? Or how is this commonly done?

Thanks.

 

[JesperMP]

The Siemens support guy is correct.
PTC Thermistors have a highly non-linear characteristic. When the temperature nears the limit, the resistance increases sharply, and triggers the alarm.
The PTC in the motor is adapted to the temperature class. So it just either "OK" or "Trip". There is no analogue temparature value.

The "Umax 30V DC PTC Thermistor" confirms that it is this kind of thermistor.

The CU240E-2 supports KTY84. It is selected with parameter p0601. Parameter r0035 then shows the actual winding temperature of the motor.
But you would have to purchase the motor with this kind of sensor.

 

[Jieve]

Jesper,

Thanks so much, exactly the answer I was looking for.