Switching between Resistance Reading Channels on DAQ6510

Hi&#160; - I have two 4W resistance channels set up, channels 201 &amp; 202. Channel 201 will be measuring high values - from 10M to Open Circuit while Channel 202 will be measuring low values - less than 2R.<br> <br> When switching from Ch 202 to CH201 the next reading of Ch201 (very occasionally two readings) will either display a -ve value of else be an incorrect value. If I repeat the measurement it will settle down to a final value. I've tried experimenting with time delay before taking the Ch201 reading but it definitely seems to require the second read rather than just time to settle. The DMM is set to Autorange.<br> <br> Have you any thoughts as to what can be going on?

What card are you using for the DAQ6510 resistance measurements?

It is a 7707 card, in slot 2<br> <br> Cheers.

How long are your cables from the 7707 and the devices?<br> <br> Also, for the high ohm channel, can you instead use 2W ohms mode?<br> I suspect part of the settling time issue will be for charging up the remote sense lines.<br> For 10M-Ohm and higher DUT value, the use of 4W is of negligible benefit and in this case might be giving you a longer settling time problem.

<p>Cables are ~ 1m. I can't use 2W as it opens switch 215 leaving the backplane in 10x2 mode rather than 5x4 which would cause issues elsewhere.</p> <p>After further investigation the parts I am measuring are 5M to 100M with a fixed parallel capacitance of 24nF, which gives a significant settling time of ~ 1sec. Nothing I have found to try within the IVI-COM driver seems to better the &quot;measure wait 1 sec and measure again&quot; method I mentioned in my OP, although this doesn't quite give the value seen with the meter running in continuous mode.</p> <p>I have tried increasing various delay functions (NPLC = 12 max, Aperture = 0.24s max, fixed range(100M) delays = 275ms max) but none are long enough to allow the reading to reach the value that it achieves when the meter is running in continuous mode. Other delay functions just seem to delay the actual taking of the measurement without the part actually being connected to the meter for the entirity of the period.</p> <p>Can you point me to an IVI-COM driver command that can allow the shunt capacitance to charge from the meter to its final value before takng&#160;the resistance measurement?</p> <p></p> <p>Thanks</p>

You may want to revisit the idea of using 2W for the high ohms channel.<br> When a measure function is associated with a channel, then when closing that channel, all the required channel pairing (in case of 4W) and backplane relays are managed for you.<br> So a scan that uses both 2W and 4W will mange the backplanes appropriately for the closed channel.<br> <br> If using a scan with mixed measure function type, I'm able to reliably measure 50MΩ (2Wire) and 0.5Ω (4Wire) on two different channels.&#160; See attached.<br> <br> If not performing a scan and attempting use of 4W with the 50MΩ, I find extra settling time is needed.<br> I'm not able to find a command in the IVI driver.&#160; So using the WriteString() to send:&#160; &quot;:ROUT:DEL 0.25, (@106)&quot;&#160; to obtain an extra 250msec on channel 106.<br> <br> See attached for info on both defining a scan or the single channel read approach.