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Connecting Sensors and Actuators to Input/Outputs
66 AX2550 Motor Controller User’s Manual Version 1.9b. June 1, 2007
Connecting External Thermistor to Analog Inputs
Using external thermistors, the AX2550 can be made to supervise the motor’s tempera-
ture and adjust the power output in case of overheating. Connecting thermistors is done
according to the diagram show in Figure 35. The AX2550 is calibrated using a 10kOhm
Negative Coefficient Thermistor (NTC) with the temperature/resistance characteristics
shown in the table below.
Thermistors are non-linear devices. Using the circuit described on Figure 35, the controller
will read the following values (represented in signed binary) according to the temperature.
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
10kOhm
10kOhm
NTC
Thermistor
Internal Resistors
and Converter
+5V 14
Ground 5
A/D
Ana 1: 11
Ana 2: 10
Ana 3: 12
Ana 4: 8
FIGURE 35. NTC Thermistor wiring diagram
-150
-100
-50
0
50
100
-20
-10
0
10
20
30
40
50
60
70
80
90
100
110
Temperature in Degrees C
Analog Input Reading
FIGURE 36. Signed binary reading by controller vs. NTC temperature