Behind the tach and hour counter, there is only a wire array connector, so I guess the signal comes from the alternator. But I don't know what kind of 'correct' signal should I expect to be coming from there in order to d鬨‘rmine wether the problem is on the meter or alternator and wire side... Should it be a voltage proportional to the engine RPM ? Or a current ? Or a time varying signal ?
Phil
Sorry about that, I was thinking the 3060 had a mechanical tach. The signal from the alternator is usually a magnetic pulse type. Best looked at with a O-scope if you can get access to one or a digital pickup frequency counter. You may not be able to lock in on the pulses but it would confirm the sending unit is working. There are some volt meters with the capability to pick up the signal.
I found this info, it may help:
Electronic tachometers work by counting pulses generated by the alternator, tach signal generator, ignition system or by a magnetic pick-up sender. By choosing the correct tachometer for your application and setting the ranging switch to the right position, you let the tachometer know how many pulses are sent for each revolution of the engine. From this information, the tachometer will display the correct engine speed. The tachometer is connected to 12 or 24 VDC, Ground and to one of the signal sources previously listed. Reference the installation instructions for your tachometer for the proper connections.
Application:
On diesel engines tachometer signal is generated by one of 3 things: 1) the alternator, 2) the magnetic sensor, which counts gear teeth, or 3) a tachometer signal generator that is spun by the mechanical take-off.
1. The diesel alternator tachometer is hooked up the AC tap of the alternator. This connection can be marked as: AC, AUX, S, R, TACH, or nothing at all. Once installed, the tachometer can be calibrated to the engine by using a shop tach, or a known 渡o load governed speed. The tachometer can be bench-calibrated by using a frequency generator and the following formula:
Full scale frequency = full scale RPM x ï½½ poles in the alternator x pulley ratio
60
There are 2 versions of the alternator tachometer the 300-900 Hz model and the 700-2100 Hz model. By using the above formula you can choose the correct tachometer for your application.
2.
The magnetic sensor tachometer is hooked up to a hall-effect sensor that counts gear teeth as they pass by the sensor. Both wires from the sensor are routed to the tachometer as a twisted pair. One wire is connected to the signal input and the other to the ground terminal on the back of the tachometer. The ranging switch code for the amount of teeth on the wheel can be found in your tachometerç—´ installation instructions.
3.
The generator driven tachometer is connected to a pulse generator, which is spun by the engineç—´ mechanical take-off. One of the wires is connected to chassis ground and the other is routed to the signal input of the tachometer. The switch for this tachometer is marked as .5:1, 1:1, 1.5:1 and 2:1. Set the selector switch to the position that corresponds to the mechanical take-off ratio of your vehicle.
Troubleshooting:
Symptom recognition and visual inspection are the steps in effective troubleshooting. A multimeter is a helpful tool when troubleshooting instrumentation, and will make the task much easier. Tachometers usually exhibit the following symptoms: 1. Dead, 2. Reading high or low, 3. Erratic.
1. Dead - this is usually caused by no power applied or by no signal applied. First, with the installation instructions, make sure the tachometer is connected properly. If the tachometer is connected properly, check the voltage between the 釘+ and 敵 terminals on the tachometer. 12-volt systems will have a voltage between 12-16 VDC; 24-volt systems will have a voltage between 22-28 VDC. If these voltages are not present check the ground and ignition connections to the tachometer and the continuity of the wires making these connections. If the voltages are present, check for the presence of a signal. Measure the signal between the 鉄IG and 敵 terminals on the tachometer. Signal strength should be in excess of 2 VDC.
2. Reading high or low
- This is usually caused by the ranging switch on the tachometer set in the wrong position or the wrong tachometer is being used for your application. Check to be sure the switch is in the correct position for your engine.
3. Erratic
- This is usually caused by a loose or intermittent connection on the back of the tachometer. Check to see if the connections are tight and that the terminal hardware is making contact with the wires conductor. In the case of the magnetic pick-up tachometer, erratic action can be caused by the wrong air-gap between the sensor and the gear teeth. A .050 air-gap is what Beede Electrical Instruments recommends. To achieve a .050 air-gap, turn the sensor into the Housing until it touches the gear teeth and then back the sensor out ï½¼ turn.
