I'm trying to determine the resistance vs. temperature relationship for the charge air temperature sensor.
I found this table in another thread (thanks Naj!):
(charge air temp sensor temperature vs. voltage)
0 deg = 4.70 volts
20 deg = 4.47
40 deg = 4.11
60 deg = 3.67
80 deg = 3.08
100 deg = 2.51
120 deg = 1.97
140 deg = 1.52
160 deg = 1.17
180 deg = .86
200 deg = .65
220 deg =.48
240 deg = .35
260 deg = .28
This table is somewhat misleading, as the sensor itself is a thermistor, and does not output a voltage on its own. These voltages are what you would measure at the 5V reference side of the thermistor while it is plugged in.
The output impedance of the 5V source was measured and determined to be 10k by placing a known resistance across the sensor pigtail with the pigtail unplugged, measuring the voltage drop across the known resistance, and then calculating the series impedance of the 5V source using ohms law.
Based on the table above, the 5V source, and the 10k output impedance of the 5V source, the following table can be generated:
Temp (F) V Rt Rt
0 4.7 156667
20 4.47 84340
40 4.11 46180
60 3.67 27594
80 3.08 16042
100 2.51 10080
120 1.97 6502
140 1.52 4368
160 1.17 3055
180 0.86 2077
200 0.65 1494
220 0.48 1062
240 0.35 753
260 0.28 593
The first two columns are the same as the first table. The third column is the calcuated resistance of the thermistor.
These values contradict the values on thedodgegarage.com which lists the following:
32F Degrees = 29,330-35,990 Ohms
77F Degrees = 9,120- 10,880 Ohms
212F Degrees = 640-720 Ohms
Anyone know why this might be?
I found this table in another thread (thanks Naj!):
(charge air temp sensor temperature vs. voltage)
0 deg = 4.70 volts
20 deg = 4.47
40 deg = 4.11
60 deg = 3.67
80 deg = 3.08
100 deg = 2.51
120 deg = 1.97
140 deg = 1.52
160 deg = 1.17
180 deg = .86
200 deg = .65
220 deg =.48
240 deg = .35
260 deg = .28
This table is somewhat misleading, as the sensor itself is a thermistor, and does not output a voltage on its own. These voltages are what you would measure at the 5V reference side of the thermistor while it is plugged in.
The output impedance of the 5V source was measured and determined to be 10k by placing a known resistance across the sensor pigtail with the pigtail unplugged, measuring the voltage drop across the known resistance, and then calculating the series impedance of the 5V source using ohms law.
Based on the table above, the 5V source, and the 10k output impedance of the 5V source, the following table can be generated:
Temp (F) V Rt Rt
0 4.7 156667
20 4.47 84340
40 4.11 46180
60 3.67 27594
80 3.08 16042
100 2.51 10080
120 1.97 6502
140 1.52 4368
160 1.17 3055
180 0.86 2077
200 0.65 1494
220 0.48 1062
240 0.35 753
260 0.28 593
The first two columns are the same as the first table. The third column is the calcuated resistance of the thermistor.
These values contradict the values on thedodgegarage.com which lists the following:
32F Degrees = 29,330-35,990 Ohms
77F Degrees = 9,120- 10,880 Ohms
212F Degrees = 640-720 Ohms
Anyone know why this might be?