How do I connect out0 to ab0 for the SCXI-1127?

[Ted Carancho]

We are using the SCXI-1331, SCXI-1127 and PXI-4070 in a PXI-1011 chassis. We are putting the SCXI-1127 in 2-wire mode to measure 30 current shunts. We would like to occasionally measure the resistance of our shunts using the 4-wire method to calibrate our system. For this calibration, we can manually connect the excitation wires from the out0 connector to the shunt. How can I route the out0 connector to the HVAB bus which will neable me to take the 4-wire resistance measurement at the 4070?

[Mike_T]

The easiest way to do this is with the switch in "Scanning" mode. In Measurement and Automation Explorer (MAX) configure each of the 1127 channels to be in 4-wire mode. When the switch is configured as such, the switch will automatically connect the AB0 and AB2. If you don't want to constantly be in 4-wire mode, then you can programmatically change the mode of the switch. Review the linked knowledge base. One note, Simulate should be equal to 0 not 1. If equal to 1 then it will run in simulation mode and then your really won't get any measurements. 😉
Knowledge Base 2LEE130A
: How Do I Change the Input Mode or Topology of a Switch Module Programmatica...


If you are programming the switch independantly then you will need to make sure that the correct bank connect relays are closed and AB2 is closed.

My recommendation would be to use scanning, then you don't have to worry about the AB relays. Once configured in 4-wire then you simply need to take your measurement with the DMM.

Good luck. Let me know if you have further questions.

Mike Taylor

[Mike_T]

Ted,
After reading my response I wanted to expound on a few things. When the switch is in scanning mode the switch closes AB0 and AB2 automically. However, they are not connected together, as it may imply by previous comment. The AB0 relay connects OUT0(Common 0) to AB0 which is where the DMM takes its voltage readings. The AB2 relay connects OUT2 to AB2, which is where the Voltage Sense is taken. I noticed that you are using 30 current shunts. You can only make 16 4-wire measurements with the 1127. This will require an additional 1127 to sample all 30 current shunts. In the 1127 manual "Using the 1127 Section: 4-wire Channel Scanning Measurement", you will find a detailed explanation of how to wire a 4-wire measurement. You will need to short the
corresponding A+ channel to the B+, short the A- to the B- of the corresponding channel. For example if you need to make a 4-wire resistance measurement on channel 1, then you will connect your resistor across channel 1. Short ch1A+(ch1+) to ch1B+(ch17+). Short channel 1A-(ch1-) to ch1B-(ch17-). This provides a path for the SENSE to take the measurement.
When you are in 4-wire mode you will not be able to reference channels above 15, because these are reserved for the SENSE channels of channels 0-15.
You can leave the wires connected when taking your normal voltage measurement because the channel relays will not be closed and you will be left with an open circuit for the SENSE channels.

Good Luck.

Mike Taylor

[David Ng]

Hi Mike,

I experienced the same problem as Ted. I'm having a hard time connecting ab0 and ab2 through the software, thus I'm getting reading that's way off and incorrect.
I'm using SCXI-1127 and 1331 and DMM HP34401A..Can you please help on how to structurize the sequence?

I already have initialized Ni-switch and DMM and it's a matter of connect the right channel so that I can command "Read" on my DMM.

Your help on this is very much appreciated

David Ng