National Instruments SCXI-1321 User Manual

SCXI -1321 OFFSET-NULL AND SHUNT-CALIBRATION HIGH-VOLTAGE TERMINAL BLOCK INSTALLATION GUIDE

This guide describes how to install and use the SCXI-1321 offset-null and

shunt-calibration terminal block with the SCXI-1121 module. You can only use the SCXI-1321 terminal block with SCXI-1121 revision modules. In addition to the 18 screw terminals, the SCXI-1321 has circuitry for offset-null adjustment of Wheatstone bridges, and a socketed shunt resistor for strain-gauge shunt calibration. This terminal block was primarily designed for Wheatstone bridge transducers such as strain gauges, although it can easily accommodate thermocouples, RTDs, thermistors, millivolt sources, volt sources, and current-loop receivers. Thermocouples have cold-junction compensation (CJC) support.

Conventions

The following conventions are used in this guide:

» The » symbol leads you through nested menu items and dialog box options

to a final action. The sequence File»Page Setup»Options directs you to pull down the File menu, select the Page from the last dialog box.

Setup item, and select Options

C or later

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This icon denotes a caution, which advises you of precautions to take to avoid injury, data loss, or a system crash. When this symbol is marked on the product, refer to the Read Me First: Safety and Radio-Frequency Interference document, shipped with the product, for precautions to take.

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as menu items and dialog box options. Bold text also denotes parameter names.

LabVIEW™, National Instruments™, NI™, ni.com™, NI-DAQ™, and SCXI™ are trademarks of National Instruments Corporation. Product and company names mentioned herein are trademarks or trade names of their respective companies. For patents covering National Instruments products, refer to the appropriate location: Help»Patents in your software, the patents.txt file on your CD, or ni.com/patents.

ni.com

January 2003

321924C-01

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What You Need to Get Started

To set up and use the SCXI-1321, you need the following items:

❑ SCXI-1321 offset-null and shunt-calibration terminal block

❑ SCXI-1321 Offset-Null and Shunt-Calibration High-Voltage

Terminal Block Installation Guide Installation Guide

❑ Read Me First: Safety and Radio-Frequency Interference

❑ SCXI chassis and documentation

❑ SCXI-1121 module (revision C or later) and documentation

❑ Numbers 1 and 2 Phillips screwdrivers

❑ 1/8 in. flathead screwdriver

❑ Long-nose pliers

❑ Wire cutter

❑ Wire insulation stripper

SCXI-1321 Terminal Block Installation Guide 2 ni.com

Connecting the Signals

Note Refer to the Read Me First: Safety and Radio-Frequency Interference document

before removing equipment covers, or connecting or disconnecting any signal wires.

To connect the signal to the terminal block, complete the following steps, referring to Figure

1. Unscrew the top-cover screws and remove the cover.

2. Loosen the strain-relief screws and remove the strain-relief bar.

3. Enable or bypass each of the nulling circuits, depending on the signal

you are measuring.

Note Disable the offset-nulling circuitry when you are not using a Wheatstone bridge or

when the excitation channel of the SCXI-1121 is in current mode.

4. Run the signal wires through the strain-relief opening. You can add

insulation or padding if necessary.

5. Prepare the signal wire by stripping the insulation no more than 7 mm

(0.28 in.).

6. Connect the wires to the screw terminals by inserting the stripped end

of the wire fully into the terminal. No bare wire should extend past the screw terminal. Exposed wire increases the risk of a short circuit and a hardware failure.

7. Tighten the screws to a torque of 0.57 to 0.79 newton-m (5 to 7 lb-in.).

8. Connect safety earth ground to the safety-ground lug. Refer to the

Read Me First: Safety and Radio-Frequency Interference document for connection information.

9. Reinstall the strain-relief bar, and tighten the strain-relief screws.

10. Reinstall the top cover, and tighten the top-cover screws.

11. Connect the terminal block to the module front connector as explained

in the

Installing the Terminal Block section.

1 as necessary:

Back View Front View

1 Strain-Relief Bar 2 Strain-Relief Screws

3 Safety-Ground Lug 4 Mating Connector

5 Thumbscrew 6 Top-Cover Screws

7 Top Cover

Figure 1. SCXI-1321 Parts Locator Diagram

SCXI-1321 Terminal Block Installation Guide 4 ni.com

5 6 8 9 10 11

3 4

7 12

17181920

1 Screw Terminals 2 Product Information 3 W1 (CH0 Null Enabled) 4 W2 (CH1 Null Enabled) 5 R3 (CH0 Null Resistor) 6 R4 (CH0 Shunt Resistor) 7 R5 (CH1 Null Resistor)

Note: R3 through R10 are socketed.

8 R6 (CH1 Shunt Resistor) 9 R7 (CH2 Null Resistor) 10 R8 (CH2 Shunt Resistor) 11 R9 (CH3 Null Resistor) 12 R10 (CH3 Shunt Resistor) 13 W5 (CJC Mode) 14 Warning Label

Figure 2. SCXI-1321 Circuit Parts Locator Diagram

Installing the Terminal Block

To connect the terminal block to the SCXI module front connector, complete the following steps:

1. Connect the module front connector to its connector on the terminal

block.

2. Make sure that the module top and bottom thumbscrews do not

obstruct the rear panel of the terminal block.

3. Tighten the top and bottom screws on the back of the terminal block to

hold it securely in place.

4. Refer to the Performed or Supported Signal Conditioning section for

information on specific signal conditioning.

15 W4 CH3 Null Enabled) 16 W3 (CH2 Null Enabled) 17 R15 (CH3 Null Potentiometer) 18 R14 (CH2 Null Potentiometer) 19 R2 (CH1 Null Potentiometer) 20 R1 (CH0 Null Potentiometer)

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