NI PXI-2501/2503 2-Wire 24×1 Multiplexer Topology

NI Switches Help

Edition Date: April 2015

Part Number: 375472H-01

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When using the NI PXI-2501/2503 as a 2-wire 24×1 multiplexer, connect your signals using the NI TB-2605 terminal block. In this topology, you can connect to a Cold-Junction Sensor Channel for cold-junction compensation. The following figure is a representation of the NI PXI-2501/2503 in this mode.

Making a Connection

The NI PXI-2501/2503 in this topology contains 24 2-wire input channels connected to a common 2-wire channel. In software, these input channels are referred to as ch<0..23> and the common channel is referred to as com0. All positive leads (CH0+ through CH23+) can connect to COM0+, and all negative leads (CH0– through CH23–) can connect to COM0–.

For example, to connect a 2-wire signal to ch5, wire the HI side to CH5+ and the LO side to CH5–. For com0, connect to COM0+ and COM0– for the HI and LO of the signal, respectively.

You can also route cjtemp to com0, which routes com0 to a temperature sensor on the NI TB-2605 terminal block. Refer to Cold-Junction Sensor Channel for more information.

During scanning, an example scan list entry is CH2->com0;. This entry routes the signal connected to CH2+ to COM0+ and the signal connected to CH2– to COM0–.

During immediate operations when calling the niSwitch Connect Channels VI or the niSwitch_Connect function with ch2 and com0, the signal connected to CH2+ is routed to COM0+ and the signal connected to CH2– is routed to COM0–. To route the signals to AB0, use the niSwitch Connect Channels VI or the niSwitch_Connect function with com0 and ab0.


The following figure and tables identify the pins for the NI PXI-2501/2503 in the 2-wire 24×1 multiplexer topology.

Caution  Do not connect to RESERVED pins.
Software Name Polarity Hardware Name
NI PXI-2501/2503
Connector Pin Number
NI TB-2605
Terminal Name
ch0 + 67 CH0+
33 CH0–
ch1 + 66 CH1+
32 CH1–
ch2 + 65 CH2+
31 CH2–
ch3 + 64 CH3+
30 CH3–
ch4 + 63 CH4+
29 CH4–
ch5 + 62 CH5+
28 CH5–
ch6 + 59 CH6+
25 CH6–
ch7 + 58 CH7+
24 CH7–
ch8 + 57 CH8+
23 CH8–
ch9 + 55 CH9+
21 CH9–
ch10 + 54 CH10+
20 CH10–
ch11 + 53 CH11+
19 CH11–
ch12 + 50 CH12+
16 CH12–
ch13 + 49 CH13+
15 CH13–
ch14 + 48 CH14+
14 CH14–
ch15 + 47 CH15+
13 CH15–
ch16 + 46 CH16+
12 CH16–
ch17 + 45 CH17+
11 CH17–
ch18 + 40 CH18+
6 CH18–
ch19 + 39 CH19+
5 CH19–
ch20 + 38 CH20+
4 CH20–
ch21 + 37 CH21+
3 CH21–
ch22 + 36 CH22+
2 CH22–
ch23 + 35 CH23+
1 CH23–
com0 + 61 COM0+
27 COM0–
ab0 + 52 AB0+
18 AB0–
No Connect1 + 60 COM1+
26 COM1–
No Connect1 + 44 COM2+
10 COM2–
No Connect1 + 43 COM3+
9 COM3–
No Connect1 + 51 AB1+
17 AB1–
1 Not used in this topology

Additional Pin References

NI PXI-2501/2503
Connector Pin Number
Signal name
7, 56 GND
68 CJS+
34 CJS-
22 1wireREF


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