| A couple of things first. I found that in the 90 model gauge it takes a drive level of around 6 volts peak to peak in order for the gauge to start working correctly. This is not the signal in hertz to drive the needle, just a peak amplitude of the signal applied. The earlier model years only take around 1.5 volts peak to peak drive voltage to start working, 5 volts being ok. The hertz needed to drive the needle depends on the gauge design itself. So if you drive the gauge with a signal of 453 hertz and you get a reading of 100 mph then it is what it is. You can't say, hey maybe I'm driving it to much. The speedometer in a Z32 gauge cluster has all fixed components. Although all gauges take the same levels of hertz to drive the needles between cars of the same year there may be a slight difference between some gauges due to component tolerances but it's a nominal value that can shift slightly up or down without having to worry much about it. If there was a large difference between gauges then a gauge may be bad. On the other hand, the tachometers have some adjustable components. Either way, before changing to an aftermarket gauge such as the one I am working on getting made, you first take readings of the current MPH position in 5mph increments with the stock gauge face in place and record those values. You then use those values to set the speed position of the new gauge tic marks. You use the same drive level in hertz but you manipulate the result that the gauge will see by tricking the gauge by changing a component in the gauge. Here is an excerpt from an instruction document for calibrating a Z32 speedometer gauge that uses the km/h scale. As you can see, it takes 508Hz to display 180 kph on the gauge. 180 kph is roughly 111 mph. So dropping to a level of 453 hertz to obtain 100 mph is not to much drive at all. ============================================= Initial Test:
Speedometer should be connected to power and signal source, using flyleads connected to the rear terminals. Take care that terminals cannot short circuit. A 5 volt square wave at a frequency of 171Hz should be applied between the input signal terminal and ground. Observe that speedometer needle deflection should indicate 60kph +/- 1 kph Adjust frequency of signal generator until needle deflection indicates 60kph and record frequency. Adjust frequency of signal generator to 288Hz. Speedometer should indicate 100kph +/- 1kph Adjust frequency of signal generator until needle deflection of speedometer indicates 100kph exactly and record frequency. Adjust frequency of signal generator to 508Hz. Speedometer should indicate 180kph +/- 4kph Adjust frequency of signal generator until needle deflection of speedometer indicates 180kph exactly and record frequency. =============================================
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02:53:01 03/17/10
