Tach and RPM?

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Copper - Posts: 118

Joined: March 07, 2005

Posted: October 27, 2005 at 12:02 AM / IP Logged

I am installing a remote starter. the problem is that it doesn't have tach learning. It has one wire names "RPM INPUT". Is it the same with TACH input? But it can not detect the TACH signal.

I called the factory. They said if RPM is reach 600RPM, the unit will think the enigne is started. I am wondering that when enigne is running, the frequncy on TACH wire is the same showing on the tachometer?

equate

Copper - Posts: 118

Joined: March 07, 2005

Posted: October 27, 2005 at 11:05 AM / IP Logged

oK, I say it in a simply way.

If there is a frequncy 60HZ on TACH wire, how much RPM frequncy on Tachometer?

What's the relationship between them? How to convert frequncy on TACH wire to RPM on tachometer?

equate

Copper - Posts: 118

Joined: March 07, 2005

Posted: November 16, 2005 at 10:30 PM / IP Logged

Anybody can give me oscilloscope record of TACH signal? Any car is fine.

Thanks a lot.

dualsport

Silver - Posts: 983

Joined: September 27, 2005

Location: United States

Posted: November 16, 2005 at 11:59 PM / IP Logged

Here's a good picture of the scope trace on the ignition primary, with description of the specific points-

equate

Copper - Posts: 118

Joined: March 07, 2005

Posted: November 17, 2005 at 12:08 AM / IP Logged

dualsport wrote:

Here's a good picture of the scope trace on the ignition primary, with description of the specific points-

Why is it becoming DC after 3ms? I don't think so. Because TACH signal is AC.

dualsport

Silver - Posts: 983

Joined: September 27, 2005

Location: United States

Posted: November 17, 2005 at 12:12 AM / IP Logged

You have to look at the timebase of the trace- were you expecting it to look like a sine wave?

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Copper - Posts: 118

Joined: March 07, 2005

Posted: November 17, 2005 at 12:19 AM / IP Logged

It should be this:

http://www.picotech.com/auto/waveforms/rpm_sensor.html

but not really sure it is measured on TACH wire or not.

dualsport

Silver - Posts: 983

Joined: September 27, 2005

Location: United States

Posted: November 17, 2005 at 12:45 AM / IP Logged

Don't think that's typical of the majority of cars; tach is usually driven from the negative side of the ignition coil or fuel injection drive. That rpm sensor signal may be for the ECU rather than the tach, but if it works, just as well.

Assume this is for a remote start function?

equate

Copper - Posts: 118

Joined: March 07, 2005

Posted: November 17, 2005 at 1:32 AM / IP Logged

dualsport wrote:

Assume this is for a remote start function?

Yes. I think so. So can you can one waveform of TACH? I dont have oscilloscope.

dualsport

Silver - Posts: 983

Joined: September 27, 2005

Location: United States

Posted: November 17, 2005 at 1:42 AM / IP Logged

If you need to find the specific wire for your car, here's a useful link for a database of cars and the location where the tach signal is accessible.

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