Other methods of connecting up the RPM feed
As well as connecting up to the ignition system, there are a number of other options for measuring RPM on engines.
- Take the signal from the drive to one of the injectors. Almost all injectors have two connections - one will be a 12v feed and the other will be switched to ground. This can work well - the only thing to be aware of is that it is very common that under overrun conditions, rev limited conditions or the interaction of traction control the injectors will be shut off completely and the RPM signal will disappear – this will result in flat line on the RPM graphs in the software.
- Use a normal hall effect “wheel speed sensor” to detect the passing of a moving metal target on the engine. Typically this would be a bolt on the front accessory drive of the engine. This is a completely reliable way to measure engine speed, the only downside here is that it requires the user to buy an extra sensor and it needs careful mounting on the engine. This might be the only option for Diesel engine installations where a tacho output isn’t available. This signal can be used directly with the low level RPM input. Information about the wheel speed sensor is included here. Note that you must have a big enough "target" to trigger from, most of our RPM inputs need at least a 1mS pulse to trigger from. Given a pulley diameter of "D" (in mm) and a maximum RPM, then the minimum target size (in mm) can be calculated from "RPM x D / 20000".
- Use the flywheel pickup. If there is a hall effect sensor fitted as standard on the engine to measure the angle of crankshaft then this can also be used directly with the low level RPM input. The main problem here is that the RPM input can only read up to about 3000 pulses per second, so unless there are only 20 pulses per revolution or less then this method isn’t suitable. Unfortunately many flywheel pickup are inductive (which are unsuitable for the DL1) and often have 35 or 60 pulses per revolution.
- Use a camshaft pickup. If this is a hall effect sensor fitted to the engine to detect camshaft angle then this can be an excellent option. As with the comments on the flywheel sensor, this will only work with hall effect not inductive sensors, however hall effect are commonly used in this application. Also the camshaft pickup normally only uses a few (often 1) pulses per camshaft revolution, so you don’t have the potential frequency overload problem you get when using the flywheel pickup.