Any clue on how to measure a digital multimeter's input impedance? I tried hooking it up to my analog meter, and reading resistance- but I pinned my analog. Apparently I'm not doing something smart.

And no, the manual doesn't tell me the rating. I have some spare injectors I'd like to test, but don't want to blow them out. They should read 15-16 ohms if they're not clogged, right?

Thanks!


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-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards

 

Yeah, it should be listed in the specifications label for the meter.

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FORMULA 350 TK
Southern California 3rd Generation F-Body OrganizationŠ

 

Usually input impedance is associated with the volts scale, as loading is a concern when making a voltage measurement. To measure the DC volts setting input impedance, put your meter on the DC volts scale, and connect a variable resistance in series with the meter and a low impedance DC power source (a 12 volt car battery is a good source). With the variable resistor in the 0 ohms position, note the voltage reading. Increase the resistance until the voltage reading is 1/2 the initial reading. Measure the resistance of the variable resistor - it should be around 10 Meg ohms for a DMM. An analog meter should be in the 10K ohm range.

If you are trying to measure the resistance of fuel injectors, you don't really need to be concerned with the input impedance of the meter. Use the low ohms scale (usually 0 to 200 ohm range). Make sure to zero the meter (anaolg), or measure the lead resistance (DMM), before taking a resistance reading.

Tim

 

TomK, there's no label on it at all! Maybe I should open it up and check the inside...

Tim, thanks alot, I'll give that measurement procedure a try. Am I correct in guessing that you want me to measure the resistance of the test leads so I can subtract it from the reading of the fuel injector?


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-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards

 

Yes, that is correct. ALso, if you don't have the manual for the meter, you may be able to obtain one from the manufacturer.

Tim

 

One more note - I just noticed you were referencing the coil resistance to the condition of the injector nozzle. The two are not related. Measuring the coil resistance verifies that the coil is not open or shorted - you may also measure the resistance between the coil and the metal case to verify that there is no short from the coil to the, but none of these tests will reveal any characteristics of the condition of the nozzle, or the flow rate of the injector.

Tim

 

No kidding! I was always told you could tell that you had a clogged injector if the resistance was higher than 15-16 ohms. I've since decided to send those injectors to Cruizin' Performance to have them flow-tested & cleaned, instead of goofing with them myself. Thanks again!


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-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards