This article gives applied hall sensor information, and a useful 'terminology' 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) - Bosch Hall-effect ignition distributors are found on many car models (from about 1985), & are fitted with (for example) a Siemens HKZ101 Hall-effect VANE position sensor. In a 4-cylinder Bosch distributor, a chopper type wheel is fitted with four metal vane segments that pass through the HKZ Hall sensor.
To modify for the purpose of aftermarket engine management computers - 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 (or Sync) signal' (therefore in the case of a 4 cylinder three vanes are removed). The single vane is used to give a HOME signal once per 360° of distributor or camshaft rotation. Note during this time the crankshaft rotates twice, 720°, being one complete 4-stroke engine cycle.
This Home/Sync signal lets the computer know a significant event is coming up (see next section 1B)).

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) comnined with 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 trigger 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, trigger wheel '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 GT 101 or 1GT1 (works on input voltage between 4.5-24 Vdc), being a quality unit using a magnetically biased Hall-effect ICand readily available. Source example RS Components stock No. 235-5706.

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 positioned in air or when passing metal.
For the examples below I will use 12Vdc 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 12V 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 mounted Honeywell GT101 is 12V 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 GT101DC Hall-effect tooth sensor aligned to the crank positioned 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 - useful on Crank or for Wheel speed sensing with GT101DC 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 a reading.

2B) ROTOR PHASING - Typically for a 4 cylinder engine, the rotor button is centrally aligned with pole 1 on the distributor cap - and should be around 22° BTDC at this point. For optimal phasing, the distributor Hall signal should occur on a falling edge at the end of a modified vane (from metal 5 V to air 0 V). The vane trailing edge = falling edge (in my case approx 78° at crank). Summary: HOME / Sync signal occurs well before rotor fires to cylinder 1.

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 gives the start of an injection or ignition firing sequence The 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) - In-Situ 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. On the distributor is 3 terminals with marks + 0 - . To test use an adjustable dc power supply. - 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.

 
Pic: Checking of trigger signal function and alignment with teeth
The trigger point of two different hall sensors mentioned in this article are checked before connecting to an aftermarket Haltech ECU. Shown in the pic is a dc power supply supplying the 2 hall sensors. 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 ECU controlled 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 July 2009