by NathanB on Tue Jan 04, 2022 3:32 pm
Hi,
Before I cover the sensor setup, first off I should raise the fact that we strongly advise against teeing into wheel speed sensors if they are still being utilised by the ABS system, as there is potential for the splicing of these signals to impact the ABS units interpretation of these signals which could potentially affect the ABS from correct operation, which is a safety issue.
A 2 wire sensor wheels speed sensors fall under 2 categories - Passive, or Active.
You have passive, which are variable reluctor or VR type sensors. These has a pernament magnet in there sensor tip, with a coil of wire wrapped around them (which is our two wires). These read a toothed wheel for their signal. Teeth passing by the sensor alter the magnetic field, generating a voltage in the wire. The output of this signal looks like a sine wave.
These sensors are wired in an M1 with 1 wire to a UDIG resource, and the other to 0V. The sensor threshold will be 0V, and the hysteresis will be an increasing value with speed, and should be typically 1/3rd of the voltage output of the waveform at that speed. The debounce will be higher at low speeds, and lower at high speeds.
An active sensor is a magneto reluctor or MR type sensor. These have a module mounted in a substrate. These read magnetic rings (in the case of wheel speed sensors, usually mounted in the bearing assembly. The magnetic ring has alternating polarity, which make the sensor output high or low, resulting in a square wave signal.
Depending on the manufacturer, these either take a 5V or 12V input on one wire, as they are a powered (active) sensor. Some sensors will have a '+' marking on the side of the connector to help identify this. Service information, or measuring a stock car will be required to identify the correct input voltage.
These sensors are wired to the M1 with the positive side of the sensor wired to the correct input voltage, and the other side of the sensor wired to a UDIG resource, with a 220 ohm pull down resistor to ground. The signal magnitude on these sensors can vary a bit, but typically read around 0.5-2.0V peak to peak. A threshold of 1.3V is a good starting point. the hysteresis can be a single value (0.1 or 0.2V is fine), and the debounce can be a single number as well, typically i start with 10us.
Scale should be left as 1.0, sensor teeth will need to be measured, or worked out from steady state driving against a known accurate source. Sample teeth is set according to requirements. (0 automatic, 1 no averaging, >1 the number of teeth you want sampled and averaged)
Pin diagnostic channels are your friend diagnosing any debounce/hysteresis/threshold issues, or calculating values.