impedance testing

[palesha]

We installed LMS successfully & did the calibration as per the manual. Then we were able to test the thielsmall parameters. Then today when we restarted the computer for further tesing we r not able to get the proper impedance curve. When testing with 2 wire method we get straight line on the screen. But if we test with 4 wire method we get the graph but the values r not proper. Not able to trace the fault. Then reinstalled the software & recalibrated but the same results. Kindly guide me in the matter.
Mahendra Palesha

[cstrahm]

Run the calibration and verify that all tests pass, both Internal and External. If the any External tests fail, then something is wrong with the card. If they all pass then it must be something in your cabling or system outside the analyzer.

[palesha]

Dear Christ,
Thanks for ur quick reply.
We calibrated LMS once more with more precision. All the tests were ok. The speaker SPL test also coming perfectly. Then when we tried to do impedance test with 2 wire method. There is no
oscillator sound coming from speakers during sweep operation.
The graph line is coming as straight line. Then we tried to do the impedance test with 4 wire method then the graph comes but
no speaker sound. The graph of 4 wire method is with low values and also no sound coming from speaker during sweep. The resistive values of impedance is very low i.e. below 1 ohm at
resonance. All the cables r ok. Now guide us what to do?
Mahendra Palesha

[cstrahm]

If all the External tests pass, then you know that the unit is putting out signal and receiving signal correctly. If you do not hear any signal from the speaker when doing an impedance test, then that suggests that you do not have the correct wires hooked up to the speaker from the Line Output. It should be Pins 2,3 connected to the speaker.

The problem is either your external wiring, or possibly how you have the analyzer control panel setup. It sounds more like a wiring problem. For impedance make sure you have the OSC output amplitude set to 5V.

[palesha]

We hv previously run the impedance test suceesfully. After that we wanted to check our DAAS32 software ( which we were using prior to LMS) for comparison. We hv used seperate cpu's for both. Hence we removed the cpu having LMS and connected Daas32 cpu. After testing with DAAS32 we finished the work on that day. Next day we once more connected LMS cpu and it was not working. We were using quickset 2wire file and 4 wire file files which has presets. Then we uninstalled & reinstalled LMS but still the same results as mentioned. If there is some setting to be checked in the Analyzer parameter window please let us know. We get untitled.lib at the start of LMS. Then we select quickset 2 wire file. Then we open analyzer parameter window. We select graph 1 & then give the sweep command. We get a straight line without any sound from the speakers. But if we test SPL level through amp then we get sound from the speakers. If u say then we can send the actual screen picture. Just give us ur email. Hope this will clear everything .
Mahendra Palesha

[cstrahm]

You have mentioned again that you can hear the SPL tests but cannot hear the Z tests. Do you understand that you must have the LMS Line Output connected directly to the speaker for a Z test? During an SPL test it is connected to the input of a power amp. I wonder if it is still connected to the amp input.

Of course with a direct Z test like this you are driving the speaker with 10mA of current direct from LMS, which is far lower than when you do the SPL testing with an amp. It will not be as loud.

Either you do not have LMS connected directly to the speaker, or you have wrong wiring to the speaker. That is the only reason you would not hear anything during a Z test, but do hear something during an SPL Test.

[palesha]

Yes, we used amp during SPL test. But during Z test we removed the amp because it is clearly mentioned in the manual. Initially when we tested successfully we were getting the sound from speakers when connected the osc output without amp. The same speaker was tested once more but this time neither the graph came on screen nor we got the sound from the speaker.
The wiring is the same during successful testing and failed testing. Almost everythiong is the same. hence we r puzzled. All tests r also showing ok. The wire is a very small length of 8" only. We will do more trial tomorrow as it is sunday. We hope we will be able to track the fault. Still needs ur advice & expertise to get success quickly.
Mahendra Palesha

[cstrahm]

As I said, if the External Calibration tests pass, then you know the LMS board is working correctly. If you cannot get a signal from the speaker then there is something wrong wth your wiring. I do not know what else it could be.

[palesha]

Atlast got the fault. I called my firiend to help me in the matter. I checked the osc. output by multimeter. But he insisted on oscilloscope. Then we were not getting waveform on oscilloscope. Then when we reversed the polarity on oscilloscope we were getting the perfect voltage waveform. Hence we checked everything & at last found poor contact on pin no.15 of LMS computer cable. we resoldered it & now everything works fine.
Thanks for ur quick reply & support.
Mahendra Palesha