National Instruments SCXI-1121 Handbuch

CALIBRATION PROCEDURE

SCXI -1121

This document contains information and instructions for calibrating the

National Instruments SCXI-1121 signal conditioning module.

Contents

Introduction............................................................................................. 2

What Is Calibration? ........................................................................ 2

Why Should You Calibrate? ............................................................ 2

How Often Should You Calibrate? .................................................. 2

Software and Documentation.................................................................. 2

Test Equipment ....................................................................................... 3

Test Conditions ....................................................................................... 3

Calibration Process ................................................................................. 4

Initial Setup...................................................................................... 4

Configuring the Half-Bridge Completion Jumpers .................. 5

Configuring the Gain Jumpers.................................................. 7

Configuring the Filter Jumpers................................................. 8

Configuring the Excitation Jumpers ......................................... 9

Verification Procedure..................................................................... 10

Verifying Analog Input Offsets ................................................ 10

Verifying Voltage Excitation Limits ........................................ 11

Verifying Current Excitation Limits......................................... 12

Adjustment Procedure...................................................................... 13

Adjusting Analog Input Offsets................................................ 13

Adjusting Voltage Excitation ................................................... 14

Adjusting Current Excitation.................................................... 15

Verifying Adjusted Values .............................................................. 15

Test Limits .............................................................................................. 16

SCXI-1121 Front and Rear Panel Diagrams........................................... 19

™

SCXI-1121 Calibration Procedure 2 ni.com

Introduction

What Is Calibration?

Calibration consists of verifying the measurement accuracy of a device

and adjusting for any measurement error. Verification is measuring the

performance of the device and comparing these measurements to the

factory specifications. During calibration, you supply and read voltage

levels using external standards, then you adjust the device calibration

constants. The measurement circuitry compensates for any inaccuracies

in the device, and returns the accuracy of the device to the factory

specifications.

Why Should You Calibrate?

The accuracy of electronic components drifts with time and temperature,

which can affect measurement accuracy. Calibration restores these

components to their specified accuracy and ensures that the device still

meets NI standards.

How Often Should You Calibrate?

Calibrate the SCXI-1121 at a regular interval as defined by the

measurement accuracy requirements of your application. NI recommends

that you perform a complete calibration at least once every year. You

can shorten this interval based on the accuracy requirements of your

application.

Software and Documentation

You do not need any special software or documentation to calibrate the

SCXI-1121. This calibration document contains all the information you

need to complete the calibration procedure. Refer to the SCXI-1121 User

Manual for more information about the SCXI-1121.

©National Instruments Corporation 3 SCXI-1121 Calibration Procedure

Test Equipment

NI recommends that you use the equipment in Table 1 to calibrate the

SCXI-1121. If these instruments are not available, use the requirements

listed in Table 1 to select a suitable substitute.

If you do not have custom connection hardware, you need the following

connectors:

• Terminal block, such as the SCXI-1320

• Shielded 68-pin connector cable

• 50-pin ribbon cable

• 50-pin breakout box

• SCXI-1349 adapter

These components give easy access to the individual pins on the

SCXI-1121 front and rear connectors.

Test Conditions

Follow these guidelines to optimize the connections and environment

during calibration:

• Keep connections to the SCXI-1121 short. Long cables and wires can

act as antennas, picking up extra noise and thermal offsets that affect

measurements.

• Use shielded copper wire for all cable connections to the SCXI-1121.

Use twisted-pair wire to eliminate noise and thermal offsets.

• Maintain the ambient temperature between 18 °C and 28 °C.

• Keep relative humidity below 80%.

• Allow a warm-up time of at least 15 minutes for the SCXI-1121 to

ensure that the measurement circuitry is at a stable operating

temperature.

Table 1. Test Equipment

Equipment

Recommended

Model Requirements

Calibrator Fluke 5700A 50 ppm

DMM NI 4070 5 1/2-digit, 15 ppm

Resistors — 120 Ωand 800 Ω, ±10%

SCXI-1121 Calibration Procedure 4 ni.com

Calibration Process

The calibration process has the following steps:

1. Initial Setup—Configure the SCXI-1121 for calibration.

2. Verification Procedure—Verify the existing operation of the

SCXI-1121. This step determines whether the SCXI-1121 is operating

within its test limits.

3. Adjustment Procedure—Perform an external calibration that adjusts

the SCXI-1121 calibration constants with respect to a known voltage

source.

4. Verifying Adjusted Values—Perform another verification to ensure

that the SCXI-1121 is operating within its test limits after adjustments.

Initial Setup

Complete the following steps to configure the SCXI-1121 for calibration.

Refer to Figure 1 for steps 1 and 2 and Figure 2 for steps 3 and 4.

1. Remove the grounding screw from the SCXI-1121.

2. Remove the cover on the SCXI-1121 so that you have access to the

potentiometers.

Figure 1. Grounding Screw and Module Cover Removal

1 Grounding Screw 2 Module Cover

©National Instruments Corporation 5 SCXI-1121 Calibration Procedure

3. Remove the side plate of the SCXI chassis.

4. Install the SCXI-1121 into the right-most slot of the SCXI chassis.

Figure 2. Side Plate Removal and Module Installation

You do not need to cable the SCXI-1121 to a DAQ device. Leave the

configuration of the digital jumpers W32, W38, and W45 unchanged

because they do not affect this calibration procedure.

Configuring the Half-Bridge Completion Jumpers

Verify that the half-bridge completion network is disabled prior to

calibrating the SCXI-1121. Refer to Figure 3 for the location of the

half-bridge completion jumpers. Refer to Table 2 for the correct jumper

settings to disable the completion network.

1 Thumbscrews 2 Right-Most Slot 3 Side Plate

MAINFRAME

SCXI

NATIONAL

INSTRUMENTS

SCXI-1121 Calibration Procedure 6 ni.com

Figure 3. SCXI-1121 Parts Locator Diagram

1 Thumbscrews

2 Voltage and Current Adjust

3 Front Connector

4 Serial Number

5 Output Null Adjust Potentiometers

6 Second-Stage Filter Jumpers

7 Rear Signal Connector

8 Product Name, Assembly Number, Revision Letter

9 SCXIbus Connector

10 Terminal Block Mounting Hole

11 Excitation Level Jumpers

12 First-Stage Filter Jumpers

13 Second-Stage Gain Jumpers

14 First-Stage Gain Jumpers

15 Half-Bridge Completion Jumpers

16 Input Null Adjust Potentiometers

17 Excitation Mode Jumpers

18 Grounding Screw

W33

W32

R12

R13

R16

R17

R26

C2 C3

W14

W15

W16

W17

W18

W19

W27

W28

W29

W36

Q14

D3 D4

D11

D14

D15 D16

U18

U24

U28

U31

U39

W26

R33

U35

R10

U15

C14

C30

Q13

R277

C24

C25

C18

C424

U38

R275

R276

Q1 U1

U19

U20

C125

W31

W30

W21

C42

U22

L1 L2

C22

C21

R274

R1 R15 R25

R35

W20

U17

R21

C19

U14

C26

W38

C85

C70

R28

R27

W35

R30

D23

C29

D29

D38

R29

D22

D37

D28

U36

R32

R31

W34

Q20D34

W49

R22

W24

R18

U25

W23

W22

R20

R19

D10

C36

W10

W11

W12

W13

U40

D21

D17

Q18

D39

C37

D30

Q16 Q17

C423

C15

C39

C38

R45

C33

D13

W25

C20

R46

C143

U51

D40

R281

W45

U61

R99

U27

U33

U9U8

R11

U21

C27

D41

U37

Q21

U48

U60

U50

C34

D19 D20

C425

C16

D18

D26

D27

D36

D35

U47

U46

C32

R23

U11

C105

D12 Q8

U30

U42

D25 Q12

D24 Q11

U41

U34

U16

U10

U23

U29

Q10

U44

U32

W37

U26

S/N

AD705

ISO122P

AD705

ISO122P

HCT08 HCT00 HC05

11 11

1111

LF347

GAINDIP

PRIMARY

GAINDIP

RES

20K

RES

20K

RES

20K

DG409

34182

34072

GAINDIP

34072

AD705

34072

RES

20K

ADG212

78M15

7915CT

AD705

HCT191

R1 R0R2

BAABCDABCDEAB

AEDBADCABAB

AB AB CDABCDEAB

RES

20K

34080

CD4047

LT-

1009

HCT03

HCT240

HCT273

ASSY181505F-01

SCXI-1121

HCT165

R42

R43

W41

Q19

R40

W42

W43

D32

D31

D33

R41

R38

R37

U43

W48W47

R39

U45

AD705

GAINDIP

34072

AD705

BAEDCBADCBA

R36

W39

W40

Q15

W46

R273

W40

W41

W42

W43

BAEDCBADCBABA

R36

Q15

W46

R273

W48W47

W39

15 11

Front Rear

©National Instruments Corporation 7 SCXI-1121 Calibration Procedure

Configuring the Gain Jumpers

Each input channel has two user-configurable gain stages. The first-stage

gain provides gains of 1, 10, 50, and 100. The second-stage gain provides

gains of 1, 2, 5, 10, and 20. The SCXI-1121 ships with the first-stage gain

set to 100 (position A) and the second-stage gain set to 10 (position D).

To change the gain setting of a specified channel on the SCXI-1121, refer

to Table 3 for the gain jumper reference designators. Refer to Figure 3 for

the location of the gain jumpers. Move the jumper to the position indicated

in Table 4.

Table 2. Completion Network Jumpers

Channel Jumpers

Enable

Completion

Disable Network

(Factory Setting)

0W1 and W2

1W17 and

W18

2W27 and

W28

3W39 and

W40

A B

1 2 3

A B

1 2 3

W18

A B

W17

1 2 3

W18

A B

W17

1 2 3

W28

A B

W27

1 2 3

W28

A B

W27

1 2 3

W40

A B

W39

1 2 3

W40

A B

W39

1 2 3

SCXI-1121 Calibration Procedure 8 ni.com

The order of the settings for the first- and second-stage gain does not matter

as long as the first-stage gain multiplied by the second-stage gain equals the

desired final gain value.

Configuring the Filter Jumpers

Each input channel also has two user-configurable filter stages. The

SCXI-1121 ships in the 4 Hz position. Refer to Table 5 for the correct

jumper setting for the desired cutoff frequency. Refer to Figure 3 for the

locations of the jumper blocks on the SCXI-1121. Verify that both filter

stages are set to the same filter setting to ensure that you achieve the desired

bandwidth.

Table 3. Gain Jumper Reference Designators

Input Channel

Number

First-Stage

Gain Jumper

Second-Stage

Gain Jumper

0W3 W4

1W19 W20

2W29 W30

3W41 W42

Table 4. Gain Jumper Positions

Gain Setting Jumper Position

First-Stage 1 D

10 C

50 B

100 A (factory setting)

Second-Stage 1 A

2 B

5 C

10 D (factory setting)

20 E

©National Instruments Corporation 9 SCXI-1121 Calibration Procedure

Configuring the Excitation Jumpers

You can configure each excitation channel of the SCXI-1121 to either a

voltage or current excitation mode. Each channel has two jumpers for this

purpose. Set both jumpers in the same mode for correct operation of the

excitation channel. Refer to Table 6 to determine how to set up the

SCXI-1121 in the desired mode. The SCXI-1121 ships to you in the voltage

mode.

Table 5. Filter Jumper Settings

Input

Channel

Number

First Filter Jumper Second Filter Jumper

4 Hz

(Factory

Setting) 4 kHz

4 Hz

(Factory

Setting) 4 kHz

0W5-A W5-B W6 W7

1W21-A W21-B W8 W9

2W31-A W31-B W10 W11

3W43-A W43-B W12 W13

Table 6. Voltage and Current Mode Excitation Jumper Settings

Excitation

Channel Jumpers

Volta g e M o de

(Factory Setting) Current Mode

0W14 and

W15

1W22 and

W23

2W34 and

W35

3W46 and

W47

W14

1 2 3

W15

1 2 3

W14

1 2 3

W15

1 2 3

W22

1 2 3

W23

1 2 3

W22

1 2 3

W23

1 2 3

W34

1 2 3

W35

1 2 3

W34

1 2 3

W35

1 2 3

W46

1 2 3

W47

1 2 3

W46

1 2 3

W47

1 2 3

SCXI-1121 Calibration Procedure 10 ni.com

Configuring the Excitation Level

Each excitation channel of the SCXI-1121 has two different current or

voltage levels. You can set a given channel to one of the following levels:

• In the current mode—0.150 mA or 0.450 mA

• In the voltage mode—3.333 V or 10 V

After selecting the excitation mode of the desired operation—voltage or

current, refer to Table 7 to set the SCXI-1121 for the level of operation. The

SCXI-1121 ships with the voltage mode set to 3.333 V.

Verification Procedure

The verification procedure determines how well the SCXI-1121 is meeting

its test limits. You can use this information to select the appropriate

calibration interval for your application.

Verifying Analog Input Offsets

Complete the following steps to verify the analog input offsets:

1. Refer to Table 12 in the Test Limits section for all acceptable settings

for the SCXI-1121. NI recommends verifying all ranges and gains, but

you can save time by checking only those ranges used in your

application.

Table 7. Excitation Level Jumper Settings

Excitation

Channel Jumpers

3.333 V or

0.150 mA

(Factory Setting) 10 V or 0.450 mA

0W16 and

W26

1W24 and

W25

2W36 and

W37

3W48 and

W49

W16

1 2 3

W26

W16

1 2 3

W26

W24

1 2 3

W25

1 2 3

W24

1 2 3

W25

1 2 3

W36

1 2 3

W37

1 2 3

W36

1 2 3

W37

1 2 3

W48

1 2 3

W49

1 2 3

W48

1 2 3

W49

1 2 3

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