Measuring an inductive camshaft sensor

Sensor information

Type: Camshaft sensor inductive
Power supply: -
Signal type: Frequency varying
Signal level: ±0.25 V minimum up to ±60 V

Workings of the inductive camshaft sensor

The inductive camshaft sensor is constructed of a permanent magnet with a coil around it. The magnetic field strength changes when a magnetism sensitive object passes trough the magnetic field of the magnet. This changing of the magnetic field induces a voltage in the coil. The polarity of the induced voltage depends on the direction of the moving object, moving away or towards the sensor. This sensor doesn't need a power supply.

In most cases the object used to influence the magnetic field is a cam on the camshaft. Instead, sometimes a metal disk with certain cutouts that pass the sensor is mounted on the camshaft. When the camshaft is rotating and the cam or disk is passing the sensor, the camshaft sensor signal will be an AC voltage of which the frequency and amplitude depend on the rotational speed of the camshaft.

Connecting the lab scope

Correct functioning of the camshaft sensor can be checked by measuring the following signal voltages, see figure 1:

Channel Probe Voltage Range
1 Red probe Signal voltage at the positive side of the sensor 2 V
Black probe Signal voltage at the negative side of the sensor
Measuring diagram
Figure 1: Measuring diagram
Measuring a working camshaft sensor
Figure 2: Measuring a working camshaft sensor

The lab scope is connected to the camshaft sensor via a Measure lead TP-C1812B and Back Probe TP-BP85. The lab scope is set to normal scope mode with the trigger-timeout at infinite. When a one-shot measurement is started with these settings, the measurement is performed when the engine is cranked.

Measuring

Figure 3 shows a waveform of a camshaft sensor of an engine during cranking. This signal can be downloaded and used to correctly set up the lab scope or as reference signal.

Download camshaft sensor measurement during cranking

Download camshaft sensor measurement on idling engine

Lab scope measurement of camshaft sensor during cranking

Figure 3: Lab scope measurement of camshaft sensor during cranking

Channel 1 (red) shows the signal voltage if the camshaft sensor. The starter motor produces a lot of noise during cranking. This noise has no influence on the performance of the engine management system. The exact amplitude is also not very important. The engine management systems uses the falling edges of the signal voltages to determine the position of the engine.

Lab scope measurement of camshaft sensor on idling engine

Figure 4: Lab scope measurement of camshaft sensor on idling engine

Figure 4 shows the camshaft sensor signal voltage of an idling engine. The amplitude and frequency are clearly higher than during cranking, due to the higher engine speed. The signal also cleaner because the starter motor is not cranking the engine.

Diagnosis

Signal values may differ on different types of engine control units and camshaft sensors. Consult ATIS for information on specific engine control units and camshaft sensors.

The following signal deviations can indicate a problem:

  • No signal:
    Cause: back probes have no connection (perform a connection test), sensor loose, sensor defective
  • Signal shows more noise than example signal:
    Cause: signal wires damaged, poor connection in connector terminals, sensor loose, sensor defective
  • Signal shows an offset:
    Cause: scope is not set to AC coupling: AC
  • Signal has faulty pattern:
    Cause: cam or disk damaged

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Disclaimer

This document is subject to changes without notification. All rights reserved.

The information in this application note is carefully checked and is considered to be reliable, however TiePie engineering assumes no responsibility for any inaccuracies.

Safety warning:

  • Before measuring, check that sources of dangerously high voltages are switched off or shielded from contact. Voltages considered to be dangerous are voltages over 30 V AC RMS, 42 V AC peak or 60 V DC.
  • Keep a clean working environment when doing measurements.
  • This measurement and procedures are a examples / measuring suggestions and are no prescribed protocols.
  • TiePie engineering can not anticipate the safety actions that need to be taken to protect persons and appliances. Before starting a measurement, check which safety measures need to be applied.