Motor Temperature Sensing

Guidance Controllers can automatically monitor the temperatures of motors and generate an error if any temperature exceeds its specified limit. To employ this feature, the motors must be equipped with analog temperature sensors and the controller must be equipped with General Purpose Analog Inputs. Different controller models are available with 0, 2 or 4 such analog inputs.

This function has been designed to operate with Philips KTY84/130 silicon temperature sensors or with any Positive Temperature Coefficient (PTC) thermistor device.

The KTY84/130 sensor is a device whose resistance changes almost linearly over its operating range. This permits the actual temperature of the motor to be read at any time to determine if the motor is close to its thermal limit. When this sensor is employed, the temperature trip point must be set in software to the maximum permitted value that is specified by the motor manufacturer.

In contrast, PTC sensors operate almost like binary switches and provide relatively little information on the instantaneous temperature of the motor. The resistance of these devices is fairly constant until the Nominal Response Temperature (NRT) is reached, at which point the resistance changes abruptly. When a motor manufacturer uses these sensors, they select a device with a NRT that is appropriate for the motor. Also, for multi-phase motors, up to 3 PTC sensors can be wired in series within the motor and can be properly handled by the Guidance Controller.

To configure motor temperature sensing, either the maximum operating temperature must be specified for motors with KTY84/130 sensors, or the number of PTC devices that are in series in a motor must be defined.

Once configured, if any motor exceeds its maximum temperature, motor power is disabled and the error code -1610 "Controller overheating" is generated.

Motor temperature monitoring is enabled by setting parameter "Max motor temperature" (DataID 10110) to a non-zero value. For KTY84/130 sensors, the actual temperature can be read from the parameter "Motor temperature" (DataID 12110).

Parameter Database ID	Parameter Name	Description
10110	Max motor temperature	If zero, motor temperature checking is disabled. If set to a value from 1 to 3, indicates the number of PTC sensors that are connected in series. If set to a value > 10, indicates that a KTY84/130 sensor is being used. The specified value is the maximum permitted motor temperature (in degrees C). If the “Motor temperature” (DataID 12110) exceeds this value, power is disabled and an error occurs.
10111	Warning motor temperature
12110	Motor temperature	If motor temperature sensing is enabled, as indicated by a non-zero "Max motor temperature" (DataID 10110) value, this parameter indicates the current motor temperature. For PTC sensors, this value is interpreted as follows: 0 If the motor temperature is in the normal operating range. 1 If the motor temperature is greater than the NRT-20 degrees. 10 If the motor temperature exceeds the NRT. In this case, power is disabled and an error is signaled. For KTY84/130 linear sensors, this value displays the motor temperature (in degrees C). If this value exceeds the value specified by "Max motor temperature" (DataID 10110), motor power is disabled and an error is generated.

Analog Input Channel Mapping

If motor temperature sensing is enabled, the first General Purpose Analog Input channel samples the temperature sensor for the motor that is connected to amplifier #1. Likewise, the 2nd, 3rd, and 4th analog inputs are assigned to the 2nd, 3rd, and 4th amplifiers respectively. The correspondence between an analog input channel and a robot axis is dictated by the parameter "Amplifier hardware channel number" (DataID 10028). For example, if the first amplifier channel is assigned to the 2nd axis of a robot, the first analog input channel will provide the temperature for the motor for the robot's second axis.

Sensor Interfacing

To connect a KTY84/130 temperature sensor you must provide an interface circuit that converts the resistance reading of the sensor into a voltage level. The table below shows the expected analog channel input voltage values for a range of temperatures:

KTY84 / 130
Temp C	Voltage
0	-6.53
10	-5.99
20	-5.41
30	-4.82
40	-4.24
50	-3.60
60	-2.98
70	-2.35
80	-1.69
90	-1.04
100	-0.36
110	0.31
120	0.99
130	1.66
140	2.33
150	3.02
160	3.70
170	4.37
180	5.05
190	5.72
200	6.39

To connect PTC sensors, you must provide an interface circuit that generates voltage levels from the sensor as show in the table below. Because the analog input is limited to +/- 10V, the threshold accuracy is reduced when using 2 or 3 sensors in series.

PTC Sensor Voltage
# Sensors	Resistance (ohms)	Voltage
1	< 250	< -9.7 V
1	> 1330	> 3.0 V
2	< 500	< -6.5 V
2	> 2660	> 10 V
3	< 750	< 3.2 V
3	> 3990	> 10 V

This drawing below illustrates an example interface circuit that can be used for both the Philips KTY40/130 sensor and a typical PTC sensor.