Issues testing a tachometer with a function generator

In summary, a person is struggling to get useful information from a tachometer and is seeking assistance in setting up their test setup. They are using a function generator to provide input, but no matter what frequency is used, the tachometer needle does not move. They are also unsure of where to connect the 12V supply and what current is being drawn. Another person with experience in tachometer design offers some suggestions and asks for more information about the function generator setup. Finally, someone inquires about the purpose of the project.
  • #1
KingNothing
882
4
I am on an assignment to test the domain of input values of a tachometer, and what output (deflection) different values correspond to. In other words, what's the minimum and maximum signals and what does the curve look like?

The trouble is I can't get ANY useful information. The tach has three inputs: Ground, +12V, and frequency. I have the output ground of the function generator connected with the ground of the tach (and the ground of the power supply), and the frequency input with the non-ground output of the FG.

No matter what frequency I use, the needle on the tach does not move. What in the world am I doing wrong here? Can anyone describe or picture in detail what they would use as their test setup?
 
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  • #2
KingNothing said:
I am on an assignment to test the domain of input values of a tachometer, and what output (deflection) different values correspond to. In other words, what's the minimum and maximum signals and what does the curve look like?

The trouble is I can't get ANY useful information. The tach has three inputs: Ground, +12V, and frequency. I have the output ground of the function generator connected with the ground of the tach (and the ground of the power supply), and the frequency input with the non-ground output of the FG.

No matter what frequency I use, the needle on the tach does not move. What in the world am I doing wrong here? Can anyone describe or picture in detail what they would use as their test setup?

What's the output amplitude of your function generator? Is it sinusoid or square wave? I'm not really familiar with automotive electronics, but just from some quick Googling, there appears to be a wide variety of tachometer schemes (some based off of Hall Effect senders, some off the alternator, ignition, etc.)
 
  • #3
KingNothing said:
I am on an assignment to test the domain of input values of a tachometer, and what output (deflection) different values correspond to. In other words, what's the minimum and maximum signals and what does the curve look like?

The trouble is I can't get ANY useful information. The tach has three inputs: Ground, +12V, and frequency. I have the output ground of the function generator connected with the ground of the tach (and the ground of the power supply), and the frequency input with the non-ground output of the FG.

No matter what frequency I use, the needle on the tach does not move. What in the world am I doing wrong here? Can anyone describe or picture in detail what they would use as their test setup?

I didn't see where you connected 12V -- I may have missed it. What current is being drawn from the 12V supply?
 
  • #4
As someone who has worked for a company which designs and manufactures tachs and speedometers I'll see if I can help. What you describe I would assume to accept a square wave input. Most of the time even if the tach is expecting a sine wave from an inductive sensor it should accept a square wave. At the very least the needle should move. If this is a modern tach it could be expecting a TTL level signal from and engine control module. Older tachs were hooked directly to the negative side of the ignition coil which is switched to ground by a set of breaker points or in the case of solid state ignition, a transistor. When hooked to the negative side of the ignition coil you could expect VERY large voltage spikes which would have to be dealt with by the input circuitry of the tach. What did you have the function generator set to do? Do you have the output offset to go between 0 and 12 volts?
 
  • #5
heh, you want to reverse engineer someone else's product? or are you working on something like a defense repair contract? if the later, it helps to know where the signal is coming from.
 

1. How do I connect my function generator to the tachometer for testing?

To test a tachometer with a function generator, you will need to connect the output of the function generator to the input of the tachometer. This can typically be done using a BNC cable or other appropriate connection cables.

2. What frequency range should I use on my function generator for testing a tachometer?

The frequency range used on the function generator will depend on the specific tachometer being tested. It is important to consult the tachometer's manual or specifications to determine the appropriate frequency range for testing.

3. How do I know if the tachometer is accurately measuring the frequency from the function generator?

To ensure accurate measurement, it is recommended to use a frequency counter in addition to the tachometer. This will allow you to compare the frequency readings from both devices and verify the accuracy of the tachometer.

4. Can I use a function generator to test a digital tachometer?

Yes, a function generator can be used to test a digital tachometer. However, it is important to ensure that the output signal from the function generator is compatible with the input requirements of the digital tachometer.

5. What are some common issues that may arise when testing a tachometer with a function generator?

Some common issues that may arise include incorrect frequency range, improper connections, and compatibility issues between the function generator and tachometer. It is important to carefully follow the instructions and specifications for both devices to avoid these issues.

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