Issue Details

What connections are required when using a switch and digital multimeter (DMM)?

Solution

When configuring a DMM and switch, two types of connections must be made:

1. Analog connections to route the signals to be measured from the Switch to the DMM
2. Digital connections to synchronize the Switch and DMM.

The signal connection (analog) is always required, and the synchronization connections (digital) are only required in some circumstances. Each type of connection is described in detail below.


Analog Signal Connections
A switch can operate as a multiplexer or matrix and each individual switch channel can be routed to a ‘com’ or common channel. The ‘com’ channel of the switch then needs to be externally connected to the DMM. 

Digital Synchronization Connections
DMMs are capable of controlling a switch by sending and receiving digital signals through one or two trigger lines - depending on the type of synchronization being used. The physical connections required to synchronize the devices are described according to hardware type below:
 

1. PXI Switch / PXI DMM: The PXI Switch / PXI DMM configuration is the simplest because all digital trigger lines are routed along the PXI backplane to each module. Thus, no external connections are required to synchronize the devices (digital communication). External connections used to route the analog signals are still required. 

 

2. SCXI Switch / PXI DMM:

This is the best and most flexible setup since you can use any of the 407x DMMs, or the 4065 DMM. This will work for configurations where a PXI chassis and a separate SCXI chassis are used. It will also work with the PXI-1050 combo chassis which has both PXI and SCXI slots. 

There are two main options to establish connectivity between the DMM and Switch.  First of all you can connect your DMM module directly to the backplane of the SCXI chassis using an SCXI-1357 High Voltage Backplane Adapter Kit.  A second option is to use a SCXI 1362 Adapter Kit. Both of these options will allow you to control the switch modules with the DMM.  These options are explored in more detail below.
 

Using the SCXI-1357

The SCXI-1357 can be used to control a number of different switches and also includes a built in high-voltage analog bus. The switch modules that can connect with a SCXI-1357 are:

• SCXI-1127
• SCXI-1128
• SCXI-1129
• SCXI-1130
• SCXI-1175
• SCXI-1166
• SCXI-1167
• SCXI-1169
• SCXI-1193
• SCXI-1194
• SCXI-1195

The key component is the auxiliary cable which connects the AUX I/O port of the DMM to the AUX I/O port of the SCXI-1357 backplane connector. 
 

Using the SCXI-1362

If your switch module cannot connect to the SCXI-1357 then you can use the SCXI-1362 Adapter Kit to connect to your DMM. The SCXI-1362 works much like the SCXI-1357 in that it uses the AUX I/O port to communicate digitally with the DMM. The switch modules that can be used with the SCXI-1362 are:

• SCXI-1160
• SCXI-1161
• SCXI-1163R
• SCXI-1190
• SCXI-1191
• SCXI-1192

Setup 2 (PXI-1052 Combo Chassis with a DAQ card)

If software timing is adequate and triggers will not need to be shared between the DMM and Switch then installing a DAQ card with local bus connectivity in the right most slot of the PXI chassis will give you the ability to control the SCXI switch modules without having to make an external digital connection. The following M series modules have a part number that includes the local bus.

• PXI-6221
• PXI-6229
• PXI-6251
• PXI-6259
• PXI-6289

Setup 3 (PXI-1052 Combo Chassis)

The PXI-1052 chassis has an AUX connector built-in on the SCXI side, but it cannot be used to control the switches in that chassis or to route trigger signals from a DMM. Therefore, a card with the local bus connections must be used if hardware scanning is desired.  A few options are: use a DAQ card with local bus connectivity, or use the PXI-4060 DMM module.
 

 

3. SCXI Switch / PCI DMM: The connections required to synchronize a SCXI switch and a PCI DMM are nearly identical to Setup 1 above. Again, a SCXI-1362 or SCXI-1357 is required to connect to the SCXI chassis. The auxiliary cable is used to connect the AUX I/O port of the PCI DMM to the AUX I/O port of the SCXI module.

Additional Information

A digital multimeter (DMM) is a very accurate device that can be used to make a variety of measurements.  Because DMMs have such high accuracy and resolution specifications they are limited in channel count.  By using a switch/DMM configuration, the channel count can be increased to a user defined number by using switches to route signals to the DMM.  
 

Analog Signal Connections Additional Information
When using the switch as a multiplexer (i.e. 1x32), only one channel is connected to the DMM. On the other hand, when a matrix configuration (i.e. 2x8 or 4x8) is used, different physical connections are required between the ‘com’ channel(s) of the switch and the DMM depending on the application.

For example, when taking a series of 4-wire resistance measurements, one might consider a 4x8 (or similar) matrix. In general a 4 wire MUX would be a better option, but either could work. In the case of a matrix, each one of the four ‘com’ channels on the switch will connect with one of the four connectors on the front panel of the DMM. Note that each of these connections must be done externally. Moreover, the only possible ‘internal’ connections between the switch and DMM are digital signals.

Digital Synchronization Connections Additional Information
In a large chassis with multiple PXI trigger busses, it is necessary to configure the trigger bus in Measurement & Automation Explorer (MAX) if the switch and DMM do not share the same trigger bus.  Please see the additional links section for more information on how to configure the trigger bus. 

When using the SCXI-1357 it is important to remember which switch modules have a HVAB (high-voltage analog bus), because all the switches that share it will be derated to the lowest common voltage rating among the switch modules. It is okay if not all the modules are connected to the HVAB, the ones that are not will not have any effect of the voltage rating.