PXI-2720 Overview

PXI-2720 Pinout


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Table 1. Signal Descriptions
Signal Description
Bx+ Positive bank connection
Bx- Negative bank connection
CHx+ Positive signal connection
CHx- Negative signal connection
HI HI input connection
HI SENSE HI sense connection
LO LO input connection
LO SENSE LO sense connection
— No connection

PXI-2720 Hardware Diagram

This figure shows the hardware diagram of the module.


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Note Resistance values are nominal. Refer to the PXI-2720 Specifications for resistor values and accuracy information.

Refer to the following list for relay names on the module.

  • kb0r0, kb0r1...kb0r7
  • kb1r0, kb1r1...kb1r7
  • kb2r0, kb2r1...kb2r7
  • kb3r0, kb3r1...kb3r7
  • kb4r0, kb4r1...kb4r7
  • kb5r0, kb5r1...kb5r7
  • kb6r0, kb6r1...kb6r7
  • kb7r0, kb7r1...kb7r7
  • kb8r0, kb8r1...kb8r7
  • kb9r0, kb9r1...kb9r7
  • kb0...kb9
  • kb0shunt...kb9shunt
  • kbc01, kbc12...kbc89
  • ktest0, ktest1...ktest5

PXI-2720 Topology

This figure describes the topology of the module.

Module software name: 2720/Independent (NISWITCH_TOPOLOGY_2720_INDEPENDENT)

The module is composed of reed relays in parallel with discrete resistors. The module has 10 channels that can nominally switch from 0 Ω to 255 Ω in 1 Ω steps.

Note NI has created a set of reference VIs that you can use to specify a desired resistance value to output or RTD temperature to simulate. Using the reference VIs is the simplest way to interact with the programmable resistor module. It is also possible to program using direct calls in NI-SWITCH, NI-DAQmx, NI Switch Executive, or an IVI switch driver. For more information, including a detailed overview of the module architecture, visit ni.com/r/272xoverview.
Note Switching inductive loads, such as motors and solenoids, can produce high-voltage transients in excess of the module's rated voltage. Without additional protection, these transients can interfere with module operation and impact relay life.

Independent Topology


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Note Bank connect relays allow adjacent banks or channels to connect together internally. For example, you can connect two or more adjacent channels together to create a potentiometer, a voltage divider, or a multi-segment resistor chain.

Making a Connection

Each 8-bit channel is composed of one bank on the module. For example, ch0 is composed of bank 0 and ch1 is composed of bank 1. NI has created a set of reference VIs that will programmatically open and close relays based on a user-specified resistance value or RTD temperature to simulate. To access these reference VIs, visit ni.com/r/272xoverview.. NI recommends using this set of reference VIs for the easiest programming experience. If not using these reference VIs, NI recommends using the low-level relay control VIs or functions instead of the connect channel VIs or functions. The DAQmx Relay API supports closing multiple relays in a single driver call, which is faster than the channel API.

When a bank relay is closed, the corresponding resistor is placed in parallel with the low resistance of the relay, which nominally equates to a zero Ω shunt. Closing any of the 8 bank relays in a given bank decreases the resistance of that bank.

For example, the following procedure uses the NI-SWITCH Relay API to short across the largest resistor in bank 0 and join bank 0 and bank 1 in series.

  1. Close b0r7 by calling the niSwitch Relay Control VI with the inputs of b0r7 and close.
  2. Close bc01 by calling the niSwitch Relay Control VI with the inputs of bc01 and close.

You can perform the same operation using the NI-SWITCH Channel API, as shown below.

  1. Connect b0->b0r7 by calling niSwitch Connect Channels VI with the inputs of b0 and b0r7.
  2. Connect b0->b1 by calling niSwitch Connect Channels VI with the inputs of b0 and b1.

Each bank is initially in a high impedance (open) state across the bank terminals. To enable the desired output channel you must first connect the bank relay, bN.

Each bank includes a shunt relay that completely bypasses the bank's string of 8 series relays. Closing the shunt relay bN->bNshunt, for example, b0->b0shunt or low-level kb0shunt, results in a low resistance across the bank, 0 Ω nominally. This allows the module to pass signals with minimal attenuation.

Note It is not necessary to close all 8 bank relays and the shunt relay. Configuring multiple banks this way can exceed the power budget of the module.

The 4-pin front panel test connector can connect to any adjacent pair of even-odd banks, allowing resistance measurements, or voltage measurements, across those two banks, for example b0 to b1, b2 to b3, b4 to b5. To connect a pair of banks to the test leads, close the appropriate test relays using the command testN->testout. For example, to measure the resistance across banks 0 and 1, call test0->testout and test1->testout. For banks 2 and 3, call test1->testout and test2->testout. Refer to the device's hardware diagram for valid test relay connections.

Note Closing multiple pairs of test relays introduces low impedance paths between banks. NI recommends disconnecting the 37-pin DSUB connector if these low impedance paths would damage your device under test or cause the current specifications of the module to be exceeded.
Note Each channel on the module exhibits an "open" when initialized, reset, and first powered on. The niSwitch Reset and niSwitch Disconnect All Channels VIs or niSwitch_reset and niSwitch_DisconnectAll functions will disconnect all relays, resulting in an open circuit on each channel.

PXI-2720 Relay Replacement

The module uses reed relays.

Note The module uses a custom lead length to meet safety standards. Trim leads per rework instructions or use one of the custom relays from the relay kit.

Refer to the following table for information about ordering replacement relays.

Replacement Relay Part Number
Coto (all relays) 9117-0001
NI relay kit (10 relays) 781451-10

The module uses lead-free assemblies. Ensure you have the following:

  • Temperature-regulated soldering iron set to 371 °C (700 °F) for lead-free solder rework
  • 96.5/3.0/0.5 Tin/Silver/Copper solder (flux core) for lead-free solder rework
  • Solder wick
  • Fine pick
  • Isopropyl alcohol
  • Cotton swabs
Note The module uses lead-free assemblies. NI recommends using lead-free solder for relay replacement on lead-free assemblies.
Notice Do not rework lead assemblies using a lead-free work station. Lead solder from the unit could contaminate the station.
Notice If a lead-free assembly is reworked with lead solder, label the assembly to indicate this. This can prevent the same unit from being reworked later on a lead-free solder station, which could contaminate the station.

Complete the following steps to disassemble your module and replace a failed relay.

  1. Ground yourself using a grounding strap or a ground connected to your PXI chassis.
    Note Properly grounding yourself prevents damage to your module from electrostatic discharge.
  2. Locate the relay you want to replace. Refer to the following figure and table for relay locations.
    Figure 1. Module Relay Map

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    Relay NameReference DesignatorRelay NameReference DesignatorRelay NameReference DesignatorRelay NameReference Designator
    kb0shunt K1kb2r2 K30kb5shunt K59 kb7r2 K88
    kb0 K2kb2r3K31kb5K60 kb7r3 K89
    kbc01 K3 kb2r4 K32kbc56 K61kb7r4 K90
    ktest0K4 kb2r5K33ktest3 K62kb7r5 K91
    kb0r0K5 kb2r6K34kb5r0K63kb7r6 K92
    kb0r1K6 kb2r7 K35kb5r1 K64kb7r7 K93
    kb0r2K7kb3shuntK36kb5r2K65kb8shunt K94
    kb0r3K8kb3K37kb5r3K66kb8 K95
    kb0r4K9kbc34K38kb5r4 K67kbc89 K96
    kb0r5K10ktest2K39kb5r5K68kb8r0K97
    kb0r6K11kb3r0K40kb5r6K69kb8r1K98
    kb0r7K12kb3r1K41kb5r7 K70kb8r2 K99
    kb1shuntK13kb3r2K42kb6shuntK71kb8r3K100
    kb1 K14kb3r3K43kb6 K72kb8r4 K101
    kbc12K15kb3r4K44kbc67K73kb8r5 K102
    test1 K16kb3r5 K45kb6r0K74kb8r6 K103
    kb1r0 K17kb3r6K46kb6r1K75kb8r7 K104
    kb1r1K18kb3r7K47kb6r2K76kb9shunt K105
    kb1r2K19kb4shuntK48kb6r3K77kb9 K106
    kb1r3K20kb4K49kb6r4K78——
    kb1r4K21kbc45K50kb6r5K79test5 K108
    kb1r5K22kb4r0K51kb6r7K80kb9r0 K109
    kb1r6K23kb4r1K52kb6r6 K81kb9r1 K110
    kb1r7 K24kb4r2 K53kb7shunt K82kb9r2 K111
    kb2shunt K25kb4r3 K54kb7K83kb9r3 K112
    kb2 K26kb4r4 K55kbc78K84kb9r4 K113
    kbc23 K27kb4r5 K56test4K85kb9r5 K114
    kb2r0 K28kb4r6 K57kb7r0K86kb9r6 K115
    kb2r1 K29kb4r7 K58kb7r1K87kb9r7 K116
  3. Remove the front panel, as shown in the following image.
    Figure 2. Removing the Front Panel

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    1. Bracket
    2. Front Panel
    3. Front Panel Overlay
    4. Screws
  4. Remove the bracket, as shown in the following image.
    Figure 3. Removing the Bracket

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    1. CA3 Digital Back End
    2. Bracket
    3. Daughter Card
    4. Screws
  5. Replace the relay as you would any other through-hole part. Trim the replaced relay leads to no more than 1 mm (0.04 in.) from the PCB.
Tip Use the NI-SWITCH Switch Soft Front Panel to reset the relay count after you have replaced a failed relay. Refer to the Switch Soft Front Panel Help for more information.