Troubleshooting: analog input tracking

[BME genuis]

I have a problem of 2 analog input channels tracking one another (Channels 6 & 7).  Channel 6 is wired to my potentiometer however Channel 7 is not wired up in the NI 1300 terminal block.  The voltage range is 0-5V.  There is actually a slight difference in their readings but they follow each other (i.e. 1.45 & 1.48).  These channels are configured in Labview 5.1.1.  Only Channel 6 is used in my code but it worries me that something is not working right especially because now Channels 12 & 13 seem to be tracking one another.
 
1)  Are the channels physically connected to one another?
 
2)  How can I check if this is a hardware or software issue?
 
Thanks guys!
 
 

[Dennis Knutson]

<a href="http://digital.ni.com/public.nsf/allkb/73CB0FB296814E2286256FFD00028DDF" target="_blank">ghosting</a>

[BME genuis]

Dennis,
That makes sense since I am using multiplexing mode in PCI-6071E.&nbsp; If ghosting is an issue with subsequent channels why not just skip a channel for each analog input.&nbsp; The reading for the channel that is wired up and being acquired is completely accurate so apparently the ghosting does not have a detrimental effect on the first channel.
This makes me wonder if this is happening also in my analog output module 1163.&nbsp; I have two channels wired up subsequent to one another to control a gas flow controller.
-Scott

[Paul C.]

Hi Scott,Ghosting is typically only an issue with higher sampling rates due to the speed of the convert clock and interchannel delay.&nbsp; All these things can be accounted for to reduce ghosting.&nbsp;&nbsp; You could skip a channel to reduce the effects but you would lose channel count.&nbsp;&nbsp; In addition, the 1163 is a digital card and shouldn't suffer the same ghosting effect as analog input.&nbsp; The same goes for analog output on our DAQ cards.&nbsp; The m-series and e-series cards use an individual digital-to-analog converter (DAC) for analog output and don't multiplex.&nbsp;&nbsp; This means they don't have any ghosting effect.I hope this helps,Paul C.Message Edited by Paul C. on 07-01-2008 09:26 AM

[BME genuis]

I am running the DAQ&nbsp;at 50 Hz.&nbsp; Does ghosting show up as two channels not only track each other but show almost the same value.&nbsp; Can you tell me the correct way to wire up leads to NI 1300 to account for these issues?&nbsp; One pair of channels (channel 13 &amp; 14)&nbsp;that are tracking one another are both wired up to NI 1300.&nbsp; They are leads from two limit switches however only when one switch is triggered do you see any response in the channels or in other words when limit switch 1 is triggered you see 5V in channel 13 &amp; 14 but when switch 2 is triggered there is no response.

[Paul C.]

Hi, The correct way to wire the NI 1300 can be seen in the manual found <a href="http://www.ni.com/pdf/manuals/322715a.pdf" target="_blank">here</a>.&nbsp; Take a look at pages 6 and 7 for instructions / pictures.&nbsp; I assume you have Switch A to channel 13 and switch B to channel 14.&nbsp; If you turn on switch B, can you see the signal on channel 14 at all?&nbsp; My first inclination would be to verify that every part in the system is working properly.&nbsp; I would first try and verify that both switches work with channels 13 and 14 seperately regardless of ghosting.&nbsp; After that is done, I would work on the ghosting problem. I'm assuming that when switch A is turned on your can see the signal response on both channels 13 and 14.&nbsp; Are the wires shielded and seperated?&nbsp; Have you tried any of the suggestions in the previously posted article?&nbsp; Regards,Paul C.

[BME genuis]

Paul,
When you turn on Switch B you do not see a response in Channel 14 at all.&nbsp; The two switches are wired in parallel with Switch A connected to Channel 13 and Switch B connected to Channel 14.&nbsp; Why would I see no response with Switch B in Labview 5.1.1?&nbsp; Is&nbsp;that channel&nbsp;not configured correctly and if not how would I go about that?
-Scott

[Paul C.]

Hi Scott, Are you sure that the switch is working properly?&nbsp; Can you change the switches out and verify?&nbsp; This would eliminate that as a possibility.&nbsp; It sounds to me that you might not be properly sampling from the channel 14.&nbsp; Have you tried using test panels in Measurement and Automation (MAX) on a single channel (13 and 14 individually) to verify?&nbsp; This can be a simple way to verify the signals coming out of the switches without the introduction of possible noise due to multiplexing.I hope this helps,Paul C.