why DMM connects r0, but when the channel connects to r1 the DMM can also obtain voltage.

[小木虫]

I connected DMM with r0 to measure voltage from different channels. Why I connected channels to r1 or r2 the DMM can also obtain voltages. More interesting, these data were very similar to the real data. Is this right?

Thanks advace.

[chericks1]

Hi  小木虫 ,

Was r0 still connected when you made the r1 and r2 connections? 

If you could provide a brief hardware schematic and simple program that shows this problem, then I'll be able to assist you further.

Best regards!

Chad Erickson

Switch Product Support Engineer

NI - USA

[小木虫]

Hi,Chad Erickson

I used the sample: niswitch DMM swtich synchronous scanning.vi to measure vlotage between several materials vs a material with a fixed potential. The red line of DMM connected to r0. The black line connected to the fixed potential material. These materials were connected to the channels of swtich.

The scan list was "c0:37->r0", after running the vi I can get 38 voltages.

 But I used soft panel to connect one of the channel to r1, and then measured the voltage changes with time, I can obtain a steady voltage which was very similar to the data measured using the above sample vi. I connected other channels to r1 and can still measure voltages (similar to the value obtained using the sample vi). 

I want to know the reason behind this phenomenon.

thanks

帖子被小木虫在 09-30-2008 12:01 AM

时编辑过了

[chericks1]

Hi 小木虫,

I am interested in the measured values. 

To confirm, you connect the DMM's HI terminal to r0 and the LO terminal to a fixed potential.  Each column is connected to a voltage potential that is referenced to the fixed potential.  After you connect a column to r0, you measure the resulting voltage.  If you disconnect the column from r0 and connect the column to r1, then you are able to measure the same voltage.  Is this correct?

Are the rows of the matrix somehow shorted together?

Can you perform the following connections using the Switch Soft Front Panel and provide me the data?

1. Verify DMM connected only to r0.

2. Connect r0->c0.

3. Record voltage measurement c0_1.

4. Disconnect r0->c0 and connect r1->c0.

5. Record voltage measurement c0_2.

6. Disconnect r1->c0.

7. Repeat steps 2-6 replacing c0 with c1 through c37.

Thanks!

Chad Erickson

Switch Product Support Engineer

NI - USA

[木虫]

Hi,Chad Erickson

I used the soft front panel to measure the potential as following:

1.  DMM connected only to r3.

2. Connect r3->c0.

3. Record voltage measurement c0_1.

4. Disconnect r3->c0 and connect r2->c0.

5. Record voltage measurement c0_2.

6. Disconnect r2->c0.

7. Repeat steps 2-6 replacing c0 with c1 through c10.

The potential changes of each channel with time were measued and one data was chosen to list below.

(a) data_1 (mV)

-1024

-1045

-1044

-1040

-1049

-1069

-1093

-1099

-1109

-1056

-1044

(b)data_2 (mV)

-1077

-1080

-1083

-1083

-1075

-1083

-1080

-1080

-1083

-1075

-1078

. data _1 were obtained by connecting c0:10->r3 using soft front panel;

data_2 were obtained by connecting c0:10->r2 using soft front panel.

The data_1 were very steady. The potential changes of each channel fluctuated a little with a scope about 5-8 mV.  The potential changes of each channel were similar to each other.

[chericks1]

Hi 木虫,

The DMM is connected to r3.

If you briefly connect the DMM HI terminal to the reference potential before measuring c0:10->r2, do these values become closer to 0 mV?

Best regards,

Chad Erickson

Switch Product Support Engineer

NI - USA

[木虫]

Hi,Chad Erickson

The value is 0 V (near several micro-voltage) when HI line connected to LO line

Best regards

小木虫

[chericks1]

Hi 木虫 ,

I expected that the value would be near 0 V when the HI line is connected to LO.  If you briefly connect HI to LO, and then disconnect HI from LO and measure c0:10->r2, do the c0->r2, c1->r2, ... , c10->r2 measured values become closer to 0 mV?

What I'm attempting to have you do is discharge the stored potential on the DMM so floating voltages do not look like previously measured voltages.

Let me know what you find!

Chad Erickson

Switch Product Support Engineer

NI - USA