From the Expert
IGTM Frequently Asked Questions
Q. What is the difference between the IGTM-1000 & IGTM-2000?A. In July of 2000 a hardware and software change was made to the IGTM. The primary change was moving to a 4MHz microcontroller from a 2MHz version to support higher performance measurements. This required some minor changes to the software. At the same time, we replaced some obsolete pre-defined timing patterns with more popular applications. Also, some minor changes were made to the scaling of several of the configuration parameters. Those changes are detailed below:
P12 - SPARK INPUT PHASE CORRECTION (scaling change)
P26 - REFERENCE INPUT PHASE CORRECTION (scaling change)
P36 - ANGLE INPUT PHASE CORRECTION (scaling change)
P46 - TRIGGER INPUT PHASE CORRECTION (scaling change)
P90 - RS-232 BAUD RATE (available baud rates)
Q. What connections do I need to provide for the IGTM in order to know my ignition timing?
A. 1) The spark event signal is used to indicate the exact moment in time when the ignition spark occurs. Three common sources for this signal are an Inductive Spark Plug Wire Sensor, direct connection to the Ignition Coil Negative Terminal, and direct connection to the Ignition Module Trigger Signal (logic-level signal from the production engine control module to the ignition module indicating when to trigger the spark; i.e. GM-EST, Ford-SPOUT/SAW). Any of these sources can be used for the Spark Event Signal. The best and easiest source is the Inductive Pickup which clamps to any spark plug wire. This sensor is offered as an optional accessory to the IGTM-2000. The Inductive Pickup also provides the best timing measurement accuracy.
Connection to the Ignition Module Trigger Signal is normally not recommended. Some ignition modules operate in a default mode under certain conditions (and control the timing internally). Under these conditions, the timing represented by this signal may not be the same as the actual ignition timing.
2) The crankshaft reference position signal(s) (possibly one or two signals) are used to measure engine RPM and indicate crankshaft angular position for ignition timing measurement. The OEM production engine position sensors (used by the engine control module) can be used for most applications. The IGTM-2000 has high impedance signal inputs and can usually be connected to these sensors in parallel with the ECM without causing any disturbances.
In general, the more pulses per crankshaft revolution, the better the transient timing measurement accuracy. The IGTM-2000 will always provide the maximum achievable transient accuracy for any given set of inputs. Therefore, the accuracy of the measured timing will always be as good or better than the timing control accuracy of the ECM.
Q. How do I connect the IGTM to an engine without a crank position sensor?
A. Here are some common scenarios:
- Connection to the engine TDC signal (used by the production ECM)
- Typically used for General Motors (REF signal) and Ford (PIP signal) engines
- Compatible with aftermarket "Crank Trigger" sensors used for racing engines
- Easy and quick installation (no additional sensors to install)
- Average transient timing accuracy (approximately +/- 1 degree)
- User-installed one pulse per crankshaft revolution sensor
- Easy and universal installation (one sensor to install)
- Compatible with all engines
- Poor transient timing accuracy (approximately +/- 2 degrees)
- Magnetic sensor installed in OEM engine timing tab sensor hole
- Easy and universal installation (push-in sensor)
- Not good for long-term running, sensor rubs (wears) on harmonic balancer
- Poor transient timing accuracy (approximately +/- 2 degrees)
- Connection to a multi-tooth patterned wheel sensor (used by the production ECM)
- Common on many newer engines
- Easy and quick installation (no additional sensors to install)
- Good transient timing accuracy (dependent on number of teeth)
- Method #1 above with additional starter ring gear tooth sensor
- Relatively easy installation (one sensor to install)
- Excellent transient timing accuracy (+/- 0.05 degrees possible)
- Method #2 above with additional starter ring gear tooth sensor
- More involved installation (two sensors)
- Compatible with all engines
- Excellent transient timing accuracy (+/- 0.05 degrees possible)
- Optical Shaft Encoder connected to engine crankshaft
- Complicated installation (mounting bracket for encoder)
- Compatible with all engines
- Best transient timing accuracy (+/- 0.05 degrees)
Q. How does a magnetic crank position sensor work?
A. Magnetic sensors, also known as VR (Variable Reluctance) sensors, are commonly used for engine position detection. They are relatively low-cost and can endure a harsher environment than active (hall-effect) sensors. A magnetic sensor typically consists of a coil of wire wound around a permanent magnet.
The output voltage amplitude of a magnetic sensor is a function of the mass and velocity of ferrous material passing through its magnetic field (near its detecting end). It functions much like a voltage "generator". When the sensor is used to detect teeth or slots on a wheel, the zero-crossing point of the output voltage normally defines the center of the tooth/slot.
All magnetic sensors are polarized. Reversing the connection to the sensor will effectively "invert" the output voltage. The IGTM-2000 can be configured to trigger on either a negative (falling) or positive (rising) zero-crossing signal. Whenever possible, it is recommended that the sensor be wired to provide a negative zero-crossing signal (this is generally the most common wiring method for most systems). When a tooth or slot approaches the sensor, the output signal should first go positive, and then negative.
The magnetic sensor should be installed using a rigid mounting bracket. Any movement or jitter of the sensor relative to the wheel will result in timing measurement inaccuracy. The clearance distance between the sensor and wheel teeth is critical. Most manufacturers of magnetic sensors provide specifications for this distance (typically 0.020"-0.060"). In general, a clearance of 0.030" should work for most applications. The closer the sensor to the wheel, the greater the output voltage and better the noise immunity. However, care should be taken so that the sensor is not installed too closely to the wheel where the teeth may strike and damage it.
Care must also be taken to insure that the wheel itself is not physically damaged (especially when using the starter ring gear). A wheel having damaged teeth or large nicks may cause false output pulses.
Q. How does a hall-effect crank position sensor work?
A. Hall-effect sensors are also commonly used for engine position detection. These sensors typically contain internal signal conditioning and have active or open-collector outputs. Because of the internal electronics, they are usually more sensitive to the environment (heat).
The advantage of hall-effect sensors is their high noise immunity. Unlike magnetic sensors, the output voltage is constant (generally a 5-12V square wave), regardless of engine speed. Maximum noise immunity is obtained when using hall-effect sensors having "flying" magnets which are attached to the wheel (as opposed to an internal magnet within the sensor). This prevents false output pulses from damaged wheels or nicked teeth.
Most hall-effect sensors require operating power (typically 5-12 VDC). This is not a problem when the IGTM-2000 is connected in parallel with a hall-effect sensor used by another device, since that device already supplies the power. If a hall-effect sensor is to be used solely with the IGTM-2000, an external power source for the sensor must be provided.
Many hall-effect sensors have open-collector outputs. An open collector output is like a switch to ground. It is either open or closed. If the IGTM-2000 is the sole device to which the sensor output is connected, a pull-up resistor to 5 volts can be activated through the configuration parameters.
The hall-effect sensor should be installed using a rigid mounting bracket. Any movement or jitter of the sensor relative to the wheel will result in timing measurement inaccuracy. The clearance distance between the sensor and wheel teeth is critical. Most manufacturers of hall-effect sensors provide specifications for this distance (typically 0.020"-0.060"). In general, a clearance of 0.030" should work for most applications. If the clearance is too large, erratic or no output pulses may result. However, care should be taken so that the sensor is not installed too closely to the wheel where the teeth may strike and damage it.
