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A switch topology is an organizational representation of the channels and relays in a switch module. The topology establishes the default states for all relays in a module and defines the channel names. Some switches can use multiple topologies or variations of each topology type. Some terminal blocks or accessories may force the switch to use a given topology or set of topologies.
For the most up-to-date list of all switches from National Instruments, visit ni.com/switches.
Table of Contents
General-Purpose Topology
A general-purpose switch card consists of a group of independent relays. These relays are typically capable of switching high (relative to the multiplexer or matrix) current loads. Examples of use include power switching (connecting power to a unit under test (UUT)) and load switching.
The Form A and Form B switches are single pole single throw (SPST) switch types. The differentiation is in the rest state. In this state, Form A switches are open. Form B switches are closed when at rest.
Form C and Form D switch operation is based on a single pole double throw (SPDT) switch. The operational difference is the Form C switch opens the connection before it closes the other connection (this is also known as break before make or BBM). The Form D switch closes both connections before opening the original connection (this is also known as make before break or MBB).
A National Instruments general-purpose card is usually composed by a series of Form A or Form C switches. The user decides which circuits to close and which input to connect at any given moment with the corresponding output. This architecture can be used to allow a current to flow through a circuit or to route a voltage from the input to the output.
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G.P. Topology
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Max Voltage
|
Max Current
(Switching/Carry) |
Module
|
|
100 Channel SPST
|
100 V CAT I
|
1 A / 1 A
|
NI PXI-2569
|
|
100 Channel SPST
|
100 V CAT I
|
1 A / 1 A
|
NI SCXI-1169
|
|
32 Channel SPDT
|
150 VDC,125 VAC CAT I
|
2A / 5A
|
NI SCXI-1166
|
|
16 Channel SPDT
|
250 V CAT II
|
2A / 5A
|
NI SCXI 1160
|
|
16 Channel SPDT
|
150 VDC, 125 VAC CAT I
|
2A / 5A
|
NI PXI-2566
|
|
16 Channel SPST
|
125 VDC, 250 VAC CAT II
|
7A / 7A
|
NI PXI-2565
|
|
8 Channel SPDT
|
250 V CAT II
|
8A / 8A
|
NI SCXI-1161
|
Multiplexer Topology
A multiplexer, or mux is a topology in which you can connect one input to multiple outputs or one output to multiple inputs. This topology is often used for scanning when you need to automatically connect a sequence of channels to a common line. This topology can also be used to synchronize source and measure connections by using a pair of multiplexers. One multiplexer would be configured as 1:N, the other as N:1. An example of this would be a scope measuring four different signals one at a time and a function generator sourcing a signal to different point on the UUT.
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Multiplexer Topology
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Max Voltage
|
Max Current
(Switching/Carry) |
Module
|
|
256x1 1-Wire,
128x1 2-Wire |
60 VDC, 30 VAC
|
400 mA / 400 mA
|
NI SCXI-1130
|
|
128x1 1-Wire
|
60 VDC, 30 VAC
|
400 mA / 400 mA
|
NI PXI-2530
|
|
64 x1 4-Wire
|
60 VDC, 30 VAC
|
400 mA / 400 mA
|
NI SCXI-1130
|
|
64x1 2-Wire
|
60 VDC, 30 VAC
|
400 mA / 400 mA
|
NI PXI-2530
|
|
64x1 1-Wire
|
250 V CAT II
|
30 mA / 30 mA
|
NI SCXI-1128
|
|
64x1 1-Wire
|
250 V CAT II
|
1 A / 2 A
|
NI SCXI-1127
|
|
48x1 1-Wire
|
10 VDC, 7 VAC
|
3 mA / 3 mA
|
NI PXI-2501
|
|
48x1 1-Wire
|
60 VDC, 30 VAC
|
1 A / 1 A
|
NI PXI 2503
|
|
32x1 4-Wire
|
60 VDC, 30 VAC
|
400 mA / 400 mA
|
NI PXI-2530
|
|
32x1 2-Wire
|
250 V CAT II
|
30 mA / 30 mA
|
NI SCXI-1128
|
|
32x1 2-Wire
|
250 V CAT II
|
1 A / 2 A
|
NI SCXI-1127
|
|
24x1 2-Wire
|
10 VDC, 7 VAC
|
3mA / 3mA
|
NI PXI-2501
|
|
24x1 2-Wire
|
60 VDC, 30 VAC
|
1 A / 1 A
|
NI PXI-2503
|
|
Sixteen 16x1
1-Wire |
60 VDC, 30 VAC
|
400 mA / 400 mA
|
NI SCXI-1130
|
|
Octal 16x1 1-Wire
|
60 VDC, 30 VAC
|
400 mA / 400 mA
|
NI PXI-2530
|
|
16x1 4-Wire
|
250 V CAT II
|
30 mA / 30 mA
|
NI SCXI-1128
|
|
16x1 4-Wire
|
250 V CAT II
|
1 A / 2 A
|
NI SCXI-1127
|
|
12x1 4-Wire
|
10 VDC, 7 VAC
|
3 mA / 3 mA
|
NI PXI-2501
|
|
12x1 4-Wire
|
60 VDC, 30 VAC
|
1 A / 1 A
|
NI PXI-2503
|
|
Octal 4x1 1-Wire
|
240 V CAT II
|
200 mA / 200 mA
|
NI SCXI-1163R
|
Matrix Topology
A matrix is one of the most flexible switching configurations. Unlike a multiplexer, a matrix can connect multiple inputs to multiple outputs organized as columns and rows. You can connect any column to any number of rows and any row to any number of columns. At each intersection of a row and column, there is a switch. When the switch is closed, the row is connected to the column.
Matrix size is often described as M rows by N columns (M x N). The figure below depicts a 1-wire, 2 x 4 matrix.
Two common matrix configurations are shown in the two figures below.
Putting instruments on the rows and the units under test (UUTs) on the columns allows for easy UUT expansion. In this example to example, we could add more UUTs with another module and would need to connect just the four rows. If we needed to add more rows for the instruments we would need to connect all of the columns.
Putting both the instruments and the UUTs on the columns of a matrix allows for further expansion of both by adding only one more module and connecting the rows. It is limited in that expansion occurs only by adding columns.
|
Matrix Topology
|
Max Voltage
|
Max Current
(Switching/Carry) |
Module
|
|
16x16 2-Wire,
Dual 8x16 2-Wire, 8x32 2-Wire |
150 V CAT I
|
1 A / 2 A
|
NI SCXI-1129
|
|
8x32 1-Wire
|
60 VDC, 30 VAC
|
400 mA / 400 mA
|
NI SCXI-1130
|
|
8x16 2-Wire
|
150 V CAT I
|
1 A / 2 A
|
NI PXI-2529
|
|
8x16 1-Wire
|
60 VDC, 30 VAC
|
400 mA / 400 mA
|
NI PXI-2530
|
|
Quad 4x16 2-Wire,
Dual 4x32 2-Wire, 4x64 2-Wire |
150 V CAT I
|
1 A / 2 A
|
NI SCXI-1129
|
|
4x64 1-Wire,
4x32 2-Wire |
60 VDC, 30 VAC
|
400 mA / 400 mA
|
NI SCXI-1130
|
|
4x32 2-Wire
|
150 V CAT I
|
1 A / 2 A
|
NI PXI-2529
|
|
4x32 1-Wire,
4x16 2-Wire |
60 VDC, 30 VAC
|
400 mA / 400 mA
|
NI PXI-2530
|
|
4x8 2-Wire
|
250 V CAT II
|
1 A / 2 A
|
NI SCXI-1127 |
|
4x8 2-Wire
|
250 V CAT II
|
30 mA / 30 mA
|
NI SCXI-1128
|
|
4x6 2-Wire
|
10 VDC, 7 VAC
|
3mA / 3 mA
|
NI PXI-2501
|
|
4x6 2-Wire
|
60 VDC, 30 VAC
|
1 A / 1 A
|
NI PXI-2503
|
Other Switch Considerations
x-Wire Switching
NI switch modules are capable of switching 1, 2, and/or 4-wires. In 1-wire mode, you connect the positive leads to the relays and the negative leads to a common connection. All signals are referenced to this common connection. All NI multiplexers, other than the NI SCXI-1163R, can operate in 1-wire mode.
Sometimes more than one signal needs to be switched at the same time. In this situation a switch that employs 2-wire or 4-wire mode can be used. In 2-wire mode, you connect both positive and negative leads to the terminals of a channel. An advantage of 2-wire switching is great common-mode noise rejection. Some applications in which 2-wire is typically used are differential measurements, low voltage, high current, and resistance measurements in the 100 – 10 M Ohm range. 4-wire mode is usually used for 4-wire resistance measurements. Two leads are used for the current excitation and another two leads are used for measuring the voltage drop across the resistor.
[+] Enlarge Image
Relay Driver
National Instruments relay drivers are the ideal choice when the current and voltage requirements for relays exceed those found in existing relay modules (or for relays embedded in a test system). Like NI switches, relay drive modules are controlled with NI-SWITCH driver software, so engineers can program external relays connected to the relay driver and standard PXI and SCXI switch modules identically. For added safety against flyback voltages, a flyback diode has been added across the relay. The SCXI-1167 has a 5 V source and the PXI-2567 has a 5 V and a 12 V source available to drive relays. The 5 V source on the SCXI-1167 can provide up to 0.75 A of current. The 5 V source on the PXI-2567 can provide up to 1.25 A of current and the 12 V source can provide 0.50 A of current.
[+] Enlarge Image
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Module
|
Max Voltage
|
Max Current
|
Channels
|
| PXI-2567 | 50 VDC | 600 mA | 64 Non-latching |
| SCXI-1167 | 50 VDC | 600 mA | 64 Non-latching |
RF Modules
The National Instruments RF (radio frequency) switch modules are ideal for expanding the channel count or increasing the flexibility of systems with signal bandwidths greater than 10 MHz. RF is not a topology but RF switches can be any topology. High-density multiplexers, dimensionally flexible sparse-matrices, and general-purpose relays are among the available configurations in PXI and SCXI switch modules. Each of these modules has been optimized for minimal insertion loss, reflection, cross-talk, and maximum isolation between channels. For more information on these parameters see the links below for the Complex RF Switching Architectures – Part I and Part II.
|
Topology
|
Max Voltage
|
Max Current
(Switching/Carry) |
Bandwidth
|
Module
|
|
36-Terminal Sparse Matrix 50/75 Ω Coaxial
|
150 V CAT I
|
500 mA / 1A
|
500 MHz
|
NI SCXI-1193
|
|
32x1 50/75 Ω Coaxial
|
150 V CAT I
|
500 mA / 1 A
|
500 MHz
|
NI SCXI-1193
|
|
18-Terminal Sparse Matrix 50/75 Ω Coaxial
|
150 V CAT I
|
500 mA / 1A
|
500 MHz
|
NI PXI-2593
|
|
Dual 16x1 50/75 Ω Coaxial
|
150 V CAT I
|
500 mA / 1 A
|
500 MHz
|
NI SCXI-1193
|
|
16x1 Terminated 50/75 Coaxial
|
150 V CAT I
|
500 mA / 1 A
|
500 MHz
|
NI SCXI-1193
|
|
16x1 50/75 Ω Coaxial
|
150 V CAT I
|
500 mA / 1A
|
500 MHz
|
NI PXI-2593
|
|
8 Channel SPDT 50 Ω Coaxial
|
30 V
|
NA** / 2 A
|
18 GHz
|
NI SCXI-1192
|
|
Quad 8x1 50/75 Ω Coaxial
|
150 V CAT I
|
500 mA / 1 A
|
500 MHz
|
NI SCXI-1193
|
|
Dual 8x1 Terminated 50/75 Ω Coaxial
|
150 V CAT I
|
500 mA / 1 A
|
500 MHz
|
NI SCXI-1193
|
|
Dual 8x1 50/75 Ω Coaxial
|
150 V CAT I
|
500 mA / 1 A
|
500 MHz
|
NI PXI-2593
|
|
8x1 Terminated 50/75 Ω Coaxial
|
150 V CAT I
|
500 mA / 1A
|
500 MHz
|
NI PXI-2593
|
|
8x1 50 Ω Coaxial |
30 V CAT I |
500 mA / 500 mA |
2.7 GHz |
NI PXI-2547 |
|
8x1 75 Ω Coaxial |
30 V CAT I |
500 mA / 500 mA |
2.5 GHz |
NI PXI-2557 |
|
Dual 6x1 50 Ω Coaxial |
90 Vrms CAT I |
1.73 Arms / 1.73 Arms |
26.5 GHz |
NI PXI-2596 |
|
6x1 50 Ω Terminated Coaxial |
90 Vrms CAT I |
1.73 Arms / 1.73 Arms |
26.5 GHz |
NI PXI-2597 |
|
Quad 4x1 Terminated 50/75 Ω Coaxial
|
150 V CAT I
|
500 mA / 1 A
|
500 MHz
|
NI SCXI-1193
|
|
Quad 4x1 50 Ω Coaxial
|
24 V
|
1 A / 1 A
|
1.3 GHz
|
NI SCXI-1190
|
|
Quad 4x1 50 Ω Coaxial |
30 V CAT I |
500 mA / 500 mA |
2.5 GHz |
NI PXI-2594 |
|
Quad 4x1 50 Ω Coaxial |
30 V CAT I |
500 mA / 500 mA |
2.5 GHz |
NI SCXI-1194 |
|
Dual 4x1 Terminated 50/75 Ω Coaxial
|
150 V CAT I
|
500 mA / 1 A
|
500 MHz
|
NI PXI-2593
|
|
Dual 4x1 75 Ω Coaxial |
30 V CAT I |
500 mA / 500 mA |
2.5 GHz |
NI PXI-2556 |
|
Dual 4x1 50 Ω Coaxial |
30 V CAT I |
500 mA / 500 mA |
2.7 GHz |
NI PXI-2546 |
|
4x1 50 Ω Coaxial
|
24 V
|
1 A / 1 A
|
1.3 GHz
|
NI PXI-2590
|
|
4x1 75 Ω Coaxial
|
30 V CAT I |
500 mA / 500 mA |
2.5 GHz |
NI PXI-2554 |
|
4x1 50 Ω Coaxial
|
30 V CAT I |
500 mA / 500 mA |
2.7 GHz |
NI PXI-2545 |
|
4x1 50 Ω Coaxial
|
30 V CAT I |
500 mA / 500 mA |
5 GHz |
NI PXI-2595 |
|
4x1 50 Ω Coaxial
|
30 V CAT I |
500 mA / 500 mA |
5 GHz |
NI SCXI-1195 |
|
4x1 75 Ω Terminated Coaxial
|
30 V CAT I |
500 mA / 500 mA |
2.5 GHz |
NI PXI-2555 |
|
Nine 3x1 50/75 Ω Coaxial (Idependant Topology)
|
150 V CAT I
|
500 mA / 1 A
|
500 MHz
|
NI SCXI-1193
|
|
Quad 3x1 50/75 Ω Coaxial (Idependant Topology)
|
150 V CAT I
|
500 mA / 1 A
|
500 MHz
|
NI PXI-2593
|
|
Quad SPDT 50 Ω Coaxial |
30 V CAT I |
500 mA / 500 mA |
2.7 GHz |
NI PXI-2548 |
|
Quad SPDT 75 Ω Coaxial |
30 V CAT I |
500 mA / 500 mA |
2.5 GHz |
NI PXI-2558 |
|
Dual SPDT 50 Ω Terminated Coaxial |
30 V CAT I |
500 mA / 500 mA |
2.7 GHz |
NI PXI-2549 |
|
Dual SPDT 75 Ω Terminated Coaxial |
30 V CAT I |
500 mA / 500 mA |
2.5 GHz |
NI PXI-2559
|
|
Dual SPDT 50 Ω Coaxial |
90 Vrms CAT I |
1.73 Arms / 1.73 Arms |
26.5 GHz |
NI PXI-2599 |
|
Dual DPST 50 Ω Coaxial |
65 Vrms CAT I |
1.25 Arms / 1.25 Arms |
26.5 GHz |
NI PXI-2598
|
Related Links:
Browse and Compare NI Switches
How to Choose the Right Relay
Selecting Switch Bandwidth
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