RoboteQ AX2550/2850 Connecting External Thermistor to Analog Inputs, Temp oC, Resistance kOhm

Connecting External Thermistor to Analog Inputs

1kOhm

+5V 14

Max Speed Adjust 10kOhm pot

Input Ana 1 11

AX2500 Internal Resistors and Converter

47kOhm

0 Adjust

100 Ohm pot

1kOhm

Tach

or Ana 2 10

Ground 5

A/D 10kOhm

47kOhm

FIGURE 30. Tachometer wiring diagram

The tachometers can generate voltages in excess of 2.5 volts at full speed. It is important, therefore, to set the potentiometer to the minimum value (cursor all the way down per this drawing) during the first installation.

Since in closed loop control the measured speed is the basis for the controller’s power out- put (i.e. deliver more power if slower than desired speed, less if higher), an adjustment and calibration phase is necessary. This procedure is described in “Closed Loop Speed Mode” on page 123.

Important Warning

The tachometer’s polarity must be such that a positive voltage is generated to the controller’s input when the motor is rotating in the forward direction. If the polarity is inverted, this will cause the motor to run away to the maximum speed as soon as the controller is powered with no way of stopping it other than pressing the emer- gency stop button or disconnecting the power.

Connecting External Thermistor to Analog Inputs

Using external thermistors, the AX2500/2850 can be made to supervise the motor’s tem- perature and adjust the power output in case of overheating. Connecting thermistors is done according to the diagram show in Figure 31. The AX2500/2850 is calibrated using a 10kOhm Negative Coefficient Thermistor (NTC) with the temperature/resistance character- istics shown in the table below. This 10kOhm thermistor model can be found at the com- ponent section of every Radio Shack stores under the product reference 271-110A.

TABLE 13. Recommended NTC characteristics

Temp (oC)	-25	0	25	50	75	100
Resistance (kOhm)	86.39	27.28	10.00	4.16	1.92	0.93

AX2500/2850 Motor Controller User’s Manual 59