Temperature Sensors
NTC type temperature sensors are very common and cheap. They are the most used in vehicle engines because they are reliable and use only 2 wires.
This type of sensor consists of an electrical resistance that varies its value in ohms according to the temperature. Being a negative temperature coefficient (NTC = negative temperature coefficient) means that the ohms decrease as the temperature increases.
They are generally specified for their resistance to 25ºC. For example, in automotive engines, 1K (1000 ohms) at 25ºC sensors are usually used. But 10K or 100K sensors are also common.
Electric connection
Accudyno system has an internal resistance that helps in the measurement of this type of sensor. The AIN2, AIN3 and AIN4 inputs can be used for the measurement of 1K NTC sensors.
To measure NTC sensors, the jumper must be placed on the board corresponding to the input to be used. Normally we deliver the board with a single jumper mounted on Jumper NTC4 to measure temperatures in AN4 and voltage in the rest of the inputs. So if you want to measure more than one temperature, you will have to bridge jumpers NTC2, NTC3 or NTC4.
| Number | Function | Jumper | Signal No. in Software |
|---|---|---|---|
| 1 | AN1 | Reserved for AFR | 1 |
| 2 | AN2 | Jumper NTC2 | 2 |
| 3 | GND | 0V | |
| 4 | AN3 | Jumper NTC3 | 3 |
| 5 | AN4 | Jumper NTC4 | 4 |
Other resistor values
In case you want to use an NTC that is not 1K, you must work in voltage mode, without applying the jumper, and place a resistor of the same value as the sensor between +5V and the corresponding input. For example for a 100K NTC sensor, use a 100K, 1% precision resistor. You should also take into account that the internal table of the software may have to be adapted to your type of sensor in order to have greater precision.
Example: NTC type temperature sensor connection in AIN4
A typical sensor is the MD-24757 which is a replacement for Bosch or Magnetti Marelli sensor used in various makes (GM/Opel, Alfa Romeo, Fiat, Lancia/Renault, Volkswagen, Ford)
Calibration
The AIN inputs assigned to a NTC temperature sensor can be configured and calibrated in the software to adapt to the non linear scale of these kind of sensors.