Using the SCXI-1160 and SCXI-1161 as a High-Voltage, High-Current Multiplexer
PrintSwitch topology:
The general-purpose switch modules consist of independent relays. The SCXI-1160 has 16 latching single-pole double throw (SPDT) relays. The SCXI-1161 contains eight non-latching SPDT relays.
A multiplexer (MUX) consists of a group of switches that can route signals from several inputs to a single output or route a single source to multiple outputs. For example, you can have signals from several different devices under test being routed one at a time to a single DMM, or you could have a single source sending a signal to multiple points/devices. You can use the MUX as a scanner when the channels are read sequentially.
A channel is the path the signal takes through the MUX.
Break-Before-Make: An architecture that has a non-shorting transition between channels. The wiring of the relays described in this document are for Break-Before-Make provided that some basic timing requirements are met as described later.
1-Wire (Single-Ended) Switching: This mode of switching has all inputs using a common reference with only the high side of the signals being switched through the MUX.
Figure 1: 1-Wire Switching
2-Wire (Differential) Switching: This mode switches both the high and low sides of the signals.
Figure 2: 2-Wire) Switching
In order to achieve a Break-Before-Make in differential mode configuration. The command to configure the path needs to be sent to all relays simultaneously. Otherwise, a situation can develop where the high of one signal is on the positive path while the low of a different signal is on the negative path. In LabVIEW, the author uses the DIO Port Write subVI to achieve this result.
For accuracy in measurements taken using a MUX, the user should verify the maximum switching rate and minimum settling time for the particular module using the specifications provided in the module user guide. This specification is dependent on the measurement accuracy required.
How to Create the Multiplexer
The relays of the modules are combined into a “tree” by having the common (COM) of each SPDT relay connected to the normally open (NO) or normally closed (NC) connection of another relay. This setup is illustrated in Figure 3, and the connection list is provided in Table 1.
Table 1: Connection List for the Individual Relays of the SCXI-1160 and SCXI-1161
SCXI-1160 (1-wire) | SCXI-1160 (2-wire) | SCXI-1161 (1-wire) | SCXI-1161 (2-wire) |
CH0 => NO(0) | CH0+ => NO(0) | CH0 => NO(0) | CH0+ => NO(0) |
 | | | |
CH1 => NC(0) | CH0- => NO(9) | CH1 => NC(0) | CH0- => NO(2) |
CH2 => NO(1) | CH1+ => NC(0) | CH2 => NO(1) | CH1+ => NC(0) |
CH3 => NC(1) | CH1- => NC(9) | CH3 => NC(1) | CH1- => NC(2) |
CH4 => NO(2) | CH2+ => NO(1) | CH4 => NO(2) | CH2+ => NO(1) |
CH5 => NC(2) | CH2- => NO(11) | CH5 => NC(2) | CH2- => NO(5) |
CH6 => NO(5) | CH3+ => NC(1) | CH6 => NO(5) | CH3+ => NO(6) |
CH7 => NC(5) | CH3- => NC(11) | CH7 => NO(7) | CH3- => NO(7) |
CH8 => NO(9) | CH4+ => NO(2) | CH8 => NC(7) | CH4+ => NC(6) |
CH9 => NC(9) | CH4- => NO(15) | COM(7) => NC(5) | CH4- => NC(7) |
CH10 => NO(11) | CH5+ => NC(2) | COM(0) => NO(3) | COM(6) => NC(1) |
CH11 => NC(11) | CH5- => NC(15) | COM(1) => NC(3) | COM(7) => NC(5) |
CH12 => NO(15) | CH6+ => NO(5) | COM(2) => NO(4) | COM(0) => NO(3) |
CH13 => NC(15) | CH6- => NO(14) | COM(5) => NC(4) | COM(1) => NC(3) |
CH14 => NO(14) | CH7+ => NO(8) | COM(3) => NO(6) | COM(2) => NO(4) |
CH15 => NO(13) | CH7- => NO(13) | COM(4) => NC(6) | COM(5) => NC(4) |
CH16 => NC(13) | CH8+ = NC(8) | COM(6) => to DMM+ | COM(3) => to DMM+ |
COM(13) => NC(14) | CH8- => NC13) | -- | COM(4) => to DMM- |
COM(0) => NO(3) | COM(8) => NC(5) | -- | -- |
COM(1) => NC(3) | COM(13) => NC(14) | -- | -- |
COM(2) => NO(4) | COM(0) => NO(3) | -- | -- |
COM(5) => NC(4) | COM(1) => NC(3) | -- | -- |
COM(9) => NO(10) | COM(2) => NO(4) | -- | -- |
COM(11) => NC(10) | COM(5) => NC(4) | -- | -- |
COM(15) => NO(12) | COM(9) => NO(10) | -- | -- |
COM(14) => NC(12) | COM(11) => NC(10) | -- | -- |
COM(3) => NO(6) | COM(15) => NO(12) | -- | -- |
COM(4) => NC(6) | COM(14) => NC(12) | -- | -- |
COM(10) => NO(7) | COM(3) => NO(6) | -- | -- |
COM(12) => NC(7) | COM(4) => NC(6) | -- | -- |
COM(6) => NO(8) | COM(10) => NO(7) | -- | -- |
COM(7) => NC(8) | COM(12) => NC(7) | -- | -- |
COM(8) => to DMM+ | COM(6) => to DMM+ | -- | -- |
COM(7) => to DMM- | -- | -- |
LabVIEW Example
A link to a LabVIEW example which uses the NI 4060 5 1/2 digit DMM to scan a SCXI-1160 or SCXI-1161 module configured as a multiplexer is provided below.
Related Links:
Scanning a SCXI-1160 or SCXI-1161 configured as a Multiplexer using a NI DMM
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