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AX2500/2850 Motor Controller User’s Manual 59
Connecting External Thermistor to Analog Inputs
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
47kOhm
10kOhm
47kOhm
1kOhm
Max Speed Adjust
10kOhm pot
0 Adjust
100 Ohm pot
1kOhm
AX2500 Internal Resistors
and Converter
Input Ana 1 11
or Ana 2 10
+5V 14
Ground 5
A/D
Ta c h
FIGURE 30. Tachometer wiring diagram