This article gives applied hall sensor information, and is a useful read for anyone seeking to understand the function of a hall sensor / multitooth trigger wheel relationship for crank based timing. The events detailed here are a typical automotive use of hall-effect sensors and their trigger inputs to engine computers. Accurate timing information from sensors and a multi-tooth setup will give smoother running right through the rev range. We can thank American physicist Edwin Hall for discovering the Hall effect.

Section 1) Description of Components for HOME (Sync) and MAIN (Ref) signals
Section 2) Description of Events
Section 3) Bench testing

Section 1) Description of Components
1A) HOME or Sync signal (Sync=synchronisation) - For example, a Volvo/Bosch ignition distributor (Bosch # 0 237 520 004) plus various other car models, come fitted with a Siemens HKZ101 Hall-effect VANE position sensor. This 4-cylinder Bosch distributor in standard form is fitted with a chopper type wheel with four metal vane segments that pass through the HKZ hall sensor. In order to setup for advanced timing information, or sequential injection, and/or direct fire ignition, only one vane is required 'to give a home signal (in the case of a 4 cylinder three vanes are removed). The single vane is setup to give a HOME signal once per 360° of distributor or cam rotation. Note during this time the crankshaft rotates twice, 720°, being one complete 4-stroke engine cycle.

1B) MAIN or Ref signal (Ref=Reference Tooth or Index tooth) - Two hardware combinations are required - for example a Hall effect gear TOOTH sensor ( popular Honeywell 1GT101DC) and a 12 tooth metal trigger wheel (30 degree spacing) mounted on the crankshaft. (Trigger wheel info down page) The Main or Ref trigger signal occurs after the Home signal. Triggering occurs each time a metal tooth on the crankshaft mounted wheel passes the tooth sensor. The signal voltage (square wave digital) is fed into the ECU together with software entries such as trigger angle or CriP, gear tooth number and offset. These inputs enable the computer to calculate the crank angle position and engine rpm for each cylinder.
I used a Honeywell Hall effect gear TOOTH sensor # 1GT101DC commonly known as GT101 (works on input voltage between 4.5-24 Vdc), being a quality unit and readily available. Source example http://www.farnell.com/ product search 731900 .

1C) Note the difference in hall sensors: The following is a good example of differences between sensors - The Siemens HKZ101 Hall sensor operates differently to the Honeywell GT101. In operation both hall-effect sensors use a change in magnetic field to produce a voltage signal, but the difference to note is they have opposite outputs when in air or when passing metal.
For the examples below I will use 5Vdc as the input and output, and 0V means close to, or near 0.
The distributor mounted HZK101 switches to 0V in air (as it responds to a magnet field on the other side) and back to 5V when the rotating metal vane blocks the magnetic field. Therefore a rising edge from air to vane OR falling edge from vane to air.
However, the crank located Honeywell GT101 is 5V in air and pulls down to 0V when a metal tooth passes, (falling edge), being magnetically biased to conduct with metal.

Distributor wheel vane is modified by removing 3 vanes (on a 4cyl) leaving only 1 vane to generate a HOME trigger signal. For optimum rotor phasing 5mm was removed from the rear (trailing edge) of the vane. Trailing edge = falling edge

Picture shows solder counterbalance on right side. A vane weighs about 1 gram, so this weight in soft solder is added to the opposite side of wheel. The counterbalance is not essential, but recommended to save wear on the distributor shaft upper bronze bush.

Pic shows Hall-effect sensor HKZ101 (top) inside distributor. Standard in Bosch distributors OEM Volvo 1988 era

Pic shows Hall-effect tooth sensor GT101DC aligned to the crank 12T wheel. Note adjustment slot in hall mount.

MoTec supplied 12 Tooth trigger wheel 360° / 12 teeth = 30° between triggers. Watercut edge finish.

TRIGGER WHEEL - Crank / wheel speed TRIGGER WHEEL MATERIAL - (Source Honeywell article Micro Switch Sensing and Control) Requires magnetic material with less than 26 gauss residual magnetization. Cold rolled steels, type 1010-1018 are ideal, or stainless steel 430 (being a Ferritic S.S. with magnetic properties) If you have access to a guass meter, you place the meter probe in a metal shield/container, reading should be around zero. Now place your metal wheel inside of shield and take reading.

2C) After the HOME signal, the next trigger received by the ECU is the MAIN / Ref from the GT101 sensor via the multi-tooth crank wheel. This trigger occurs on the compression stroke and the angle BTDC at the crankshaft gives the ECU the all important reference position to TDC. I used a falling edge (5 V to 0 V).
For the GT101, the Hall goes from 5 V air to ~0 V over the metal tooth, hence the electrical signal is falling edge (detected on the leading edge of the tooth), and rising edge again (as it leaves the tooth's trailing edge). In your computer software you need to enter the edge you decide, bearing in mind the Honeywell sensor response time is faster on a Falling edge 1 usec max, vs Rising edge 15 usec max.

For the trigger angle, the ECU needs to know exactly how many degrees are between the index tooth triggering and #1 cylinder TDC CriP, ..deg, Tooth offset =.....The ECU then fires each ignition / or fuel output channel sequentially until it gets to the last output channel, expecting to receive another HOME signal before the sequence repeates.

The following Crank Reference Index Position (CRiP) information (Source: MoTec definitions) is a definitive statement and has been included for additional clarity.
The Crank index Position (CRiP) is perhaps the most important timing value in the ECU. The CRiP tells the ECU where the engine is in relation to TDC Cylinder #1. The CRiP is defined as the distance in crankshaft degrees, between the reference tooth when it is aligned with the crankshaft position sensor, and Top Dead Center Compression Number 1. For example, if the reference tooth is aligned with the crankshaft sensor when the crankshaft is 55 degrees before TDC Compression Number 1, then the CRiP is 55. An easy way to determine the CRiP before startup is to rotate the crankshaft in the direction of rotation until the reference tooth is aligned with the crankshaft position sensor. Then measure the number of degrees, required to turn the crankshaft in the direction of rotation until the number 1 cylinder is at Top Dead Center of the Compression stroke. Once you determine this value, you may start the engine and enter the CRiP set screen under the Ignition menu. Use a non dial-back timing light to check the CRiP. The timing advance displayed in the CRiP set screen should match the measured value using the timing light. If they do not match, move the CRiP value until the timing does match.

Section 3) Bench testing
Step 1 is to find out the connector pin function. For bench testing of a hall effect sensor, the 3 wires are : voltage input wire +Vdc, return wire -V, and a signal output wire. Before connecting, a 1 K ohm resistor load must be placed between the voltage input wire and the signal output wire. A typical voltage input is between 5Vdc and 12Vdc. As the rotor vane passes through the hall sensor a change in voltage will occur.

 
Checking the trigger signal function and alignment - The trigger point of two different hall sensors are checked before connecting to a Haltech computer. Testing dc voltage input shows near 12Vdc. Note: Before connecting, a 1 K ohm resistor 'load' must be placed between the voltage input wire and the signal output wire.

FIRING ORDER and sequence: Engine example 4 cylinder, 4 stroke cycle, typical firing order 1-3-4-2 .To complete a 4-stroke cycle, the crankshaft rotates 720 degrees, or two turns. The ignition distributor, or cam, rotates at half-speed or 1 turn for 360°. A four cylinder has 720/4=180 degrees between firing.
The firing order is the order the ignition system sends a spark to each of the cylinders via a distributor cap and rotor, or direct from coil packs.
Specs: Trigger wheel eg 12 teeth at 30 deg intervals. On an oscilloscope a Hall effect sensor signal is a square wave. The falling edge at the distributor must not occur at the same time as the trigger wheel, this will confuse the computer. Correct phasing is essential.
- To be continued.

Updated Nov 2007