SMART TUNER SMT8-L - CALIBRATION OF AIRFLOW

& TEMPERATURE SENSORS

Perfect Power Application Notes.

 

Application Note - AN 4

Introduction

The SMT8-L can read all sorts of sensors which can make the tuning easier. We can claim that the unit is compatible with such a wide range of sensors for two reasons :
  • Most sensors have an analog range between 0-5V, with exception of the frequency-based signals.
  • We can calibrate the software to read a portion of the 0-5V range, it makes better sense to adjust the sensor range to read between 2-3V if the sensor being used only moves between 2-3V.

 

It is the ability to calibrate the sensor curves that gives it flexibility by we have found that it is also a bit difficult to understand, hence this application note.

Diagrams

The following diagrams show the installation of Perfect Power Map sensor and temperature sensor.
SMT8-L Piggy-Back Unit - Wiring of Perfect Power MAP Sensor
 
SMT8-L Piggy-Back Unit - Wiring of Perfect Power Air and Engine Temperature Sensors
 

Manifold Pressure Calibration

 

SMT8-L Piggy-Back Unit - ShiftF4 - AMP Calibration

 

 

Normally Aspirated Calibration 0-1bar

To calibrate the software you need two points, a low voltage and a high voltage. With the Ignition on and the SMT8-L powered up the sensor will generate a voltage. This voltage represents the atmospheric pressure. This unit is being setup at an altitude of 1600 meters above sea level. In the screen shot above we have used a 2.5bar sensor and at a pressure of 0.84 the sensor generates 1.53 volts. This voltage is entered into the "high calibration volts". The position must not be 24 because this is being setup at altitude and not at the coast where the SMT8-L might find itself one day. At the coast the pressure will increase to 1 bar and the voltage will increase accordingly. For this reason the position chosen is 21 and the "BAR" is set at 0.84 and at the coast the sensor will read up to position 24. The "lower calibration volts" can be guessed and fine tuned once you have taken the engine to maximum vacuum and recorded the voltage of the map sensor. You can start with a voltage of 0.2 at position 1 with a BAR value of 0.20.
Note : 1 bar map sensors usually have a voltage of +- 4-5 volts at atmospheric pressure.

Forced Induction Calibration above 1 bar

To calibrate the software you need two points, a low voltage and a high voltage. With the Ignition on and the SMT8-L powered up the sensor will generate a voltage. This voltage represents the atmospheric pressure. In the screenshot above we have used a 2.5 bar sensor and at a pressure of 0.84 the sensor generates 1.53 volts. This voltage is entered into the "high calibration volts". The position must not be 24 because this is being setup for pressures above the atmospheric pressure (BOOST). For this reason the position chosen is 8 and the "BAR" is set at 0.84. The Software will calculate position 24 automatically, once you have gone to your desired highest boost and recorded the map sensor voltage for that boost you can then fine tune the high calibration setting. The "lower calibration volts" can be guessed and fine tuned once you have taken the engine to maximum vacuum and recorded the voltage of the map sensor. You can start with a voltage of 0.2 at position 1 with a BAR value of 0.20.
Note : 2.5 bar map sensors usually have a voltage of 4.8 volts at 1.5 bar boost. We don't work with negatives to represent vacuum so at 1.5 bar boost we display 2.5 bar. The boost is added to the atmospheric pressure.

Engine Temperature Calibration

NTC (negative temperature coefficient) sensors can only be used. These sensors have a high voltage when cold and a low voltage when hot. The LetRipp software will not accept a higher voltage in the high calibration than in the low calibration. To setup the high calibration place the engine temperature sensor in boiling water (+-100 Deg C) and measure the voltage the sensor generates. It should be a low voltage between 0-1.5 Volts. Take this voltage and type it into the High Calibration Volts. Assuming the engine will get hotter than 100 Deg C, enter 100 at position 22.
The Low calibration can be set for room temperature. Measure the voltage from the temperature sensor at room temperature and put that voltage into the low calibration volts. The voltage for room temp can vary from +- 3-4.3 Volts. Depending on where the car will live the rest of its life the engine temp could be exposed to temperatures lower than the measured room temp. Normally position 5 is recommended for room temp calibration but you can choose any position to suit your climate.
SMT8-L Piggy-Back Unit - ShiftF5 - Engine Temperature Calibration

Air Temperature Calibration

Setup is the same as for engine temperature. Only for forced induction engines the high calibration point should be position 18-20.