NATIONAL INSTRUMENTS SCXI-1104-C 32-Channel Medium Voltage Input Module Instruction Manual

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CALIBRATION PROCEDURE

SCXI™-1104/C

For NI-DAQmx

This document contains information and instructions for calibrating the National Instruments SCXI-1104/C signal conditioning module.

Conventions

The following conventions are used in this document:

»                        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 Setup item, and select Options from the last dialog box.

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bold                  Bold text denotes items that you must select or click in the software, such as menu items and dialog box options. Bold text also denotes parameter names.

italic                   Italic text denotes variables, emphasis, a cross- reference, or an introduction to a key concept. Italic text also denotes text that is a placeholder for a word or value that you must supply.

monospace       Text in this font denotes text or characters that you should enter from the keyboard, sections of code, programming examples, and syntax examples. This font is also used for the proper names of disk drives, paths, directories, programs, subprograms, subroutines, device names, functions, operations, variables, filenames, and extensions.

monospace italic     Italic text in this font denotes text that is a placeholder for a word or value that you must supply.

Software

The SCXI-1104/C calibration procedure requires the NI-DAQmx driver. NI recommends using the latest driver that supports both your development environment and the SCXI-1104/C. NI-DAQmx includes high-level function calls to simplify the task of writing software to calibrate devices. NI-DAQmx supports many programming languages, including LabVIEW, LabWindows™/CVI™, C/C++, C#, and Visual Basic .NET.

Documentation

The following documents are the primary references for writing your calibration utility:

• The NI-DAQmx Help includes information about creating applications that use NI-DAQmx.
• The NI-DAQmx C Reference Help includes information about the functions in NI-DAQmx.
• The DAQ Getting Started guides include information about installing and configuring NI-DAQmx devices.

You can access these documents by selecting Start»All Programs»National Instruments»NI-DAQmx after installing NI-DAQmx.

For more information about the SCXI-1104/C, refer to the SCXI-1104/C User Manual. For information about installing and configuring SCXI modules, refer to the SCXI Quick Start Guide.

Calibration Interval

Calibrate the SCXI-1104/C 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.

Password

The default password for password-protected operations is NI.

Test Equipment

NI recommends that you use the equipment in Table 1 to calibrate the SCXI-1104/C. If these instruments are not available, use the requirements listed in Table 1 to select a suitable substitute.

Table 1. Test Equipment

Equipment

| Recommended Model|

Requirements

---|---|---
Calibrator|

Fluke 5700A

|

50 ppm

DAQ Device|

NI 6281

|

16-bit minimum

DMM|

NI 4070

|

6 1/2 digit, 15 ppm

Terminal Block|

SCXI-1300

|

—

          Note   A complete SCXI-1104/C calibration system is illustrated in Figure 1 with a listing of all the components required for calibrating the SCXI-1104/C.

Test Conditions

Follow these guidelines to optimize the connections and the environment during calibration:

• Keep connections to the SCXI-1104/C as short as possible. 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-1104/C. 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-1104/C and 30 minutes for the DAQ device to ensure that the measurement circuitry is at a stable operating temperature.

Calibration Process

The calibration process has the following steps:

1. Initial Setup —Configure the SCXI-1104/C for calibration.
2. Verification Procedure —Verify the existing operation of the SCXI-1104/C. This step determines whether the SCXI-1104/C is operating within its test limits.
3. Adjustment Procedure —Perform an external calibration that adjusts the SCXI-1104/C calibration constants with respect to a known voltage source.
4. Verifying Adjusted Values —Perform another verification to ensure that the SCXI-1104/C is operating within its test limits after adjustments.

Initial Setup

Complete the following steps to configure the SCXI-1104/C for calibration:

1. Make sure that all the appropriate driver and application software is installed.
2. Make sure all components involved in the calibration procedure are powered off.
3. Assemble the SCXI-1104/C, SCXI chassis, terminal blocks, and DAQ device as shown in Figure 1. You must cable the SCXI-1104/C directly to the DAQ device. Install the SCXI-1104/C module in slot 1 of the SCXI chassis.

1  SCXI-1300 Terminal Block
2  SCXI-1104/C Module
3  SCXI Chassis
4  SCXI-1349 Cable Adapter| 5  Shielded 68-Pin Cable
6  NB1 Cable (50-Pin Ribbon Cable)
7  CB-50 Connector Block
8  Cable to DMM| 9   Cable to Calibrator
10  Calibrator
11  DMM
12  DAQ Device
---|---|---

Figure 1. Calibration Components and Connections

4. Power on the SCXI chassis and the external computer.
5. You must configure the hardware properly with Measurement & Automation Explorer (MAX). Refer to the SCXI Quick Start Guide for details about configuring the SCXI chassis.

          Note   When you configure a device in MAX, the device is assigned a device identifier. In this calibration document, the functions used for demonstrating the calibration process use the device identifiers Dev1 for the DAQ device and SC1Mod1 for the SCXI-1104/C. If you have more devices in your setup, use MAX to identify your DAQ device name.

Verification Procedure

The verification procedure determines how well the SCXI-1104/C is meeting its test limits. You can use this information to select the appropriate calibration interval for your application.

The SCXI-1104/C stores gain and offset calibration constants for each gain setting per analog input channel. A complete verification of the inputs involves measuring the accuracy at all possible gain settings on all channels of the SCXI-1104/C.

To view the calibration VIs in LabVIEW, select Measurement I/O»DAQmx – Data Acquisition»DAQmx Advanced»DAQmx Calibration on the Functions palette. You can also use the Search button, shown in Figure 2, to look for a specific VI.

Figure 2. DAQmx Calibration Palette and the Search Button

Complete the following steps to verify the accuracy of each SCXI-1104/C analog input channel:

1. Use the DAQmx Self Calibrate VI to verify the DAQ device. This VI measures the onboard reference voltage of the DAQ device and adjusts the self- calibration constants to account for any errors caused by short-term fluctuations in the operating environment.

          Note   Throughout the verification procedure, refer to the function call parameters for the LabVIEW input values.

Device_Name: “Dev1”

2. Connect the calibrator output to pins CH-­ and CH+ for all channels. Refer to the SCXI-1300/1301 Terminal Block Installation Guide for connection instructions. If you are not using the recommended SCXI-1300, refer to Table 4 for the front signal pin assignments of the SCXI-1104/C. If the calibration signal source is floating, connect CH – to the SCXI chassis ground using the ground lug available on the SCXI terminal block.
3. Set the calibrator voltage to the desired test point indicated in Table 3.
4. Create a task using DAQmxCreateTask.

parameters:
taskName: “AIVerificationTask”
taskHandle: &taskHandle

5. Add a voltage channel using the DAQmx Create Virtual Channel VI.

| Call DAQmxCreateAIVoltageChan with the following parameters:
taskHandle: taskHandle
physicalChannel: “SC1Mod1/aiX”†
nameToAssignToChannel: “myVoltageChannel”
terminalConfig: DAQmx_Val_Cfg_Default
minVal: -45 V
maxVal: 45 V
units: DAQmx_Val_Volts
customScaleName: ” “†Where X refers to the channel you are verifying.

6. Configure timing for the voltage acquisition using the DAQmx Timing VI.

LabVIEW Block Diagram

|

NI-DAQmx Function Call

---|---
| Call DAQmxCfgSampClkTiming with the following parameters:
taskHandle: taskHandle
source: ” ”
rate: 1000.0
activeEdge: DAQmx_Val_Rising
sampleMode: DAQmx_Val_FiniteSamps
sampsPerChan: 1000

7. Commit the verification changes using the DAQmx Control Task VI.

LabVIEW Block Diagram

|

NI-DAQmx Function Call

---|---
| Call DAQmxTaskControl with the following parameters:
taskHandle: taskHandle
action: DAQmx_Val_Task_Commit

8. For each new test point, use the Time Delay Express VI to account for the settling time of the SCXI-1104/C.

LabVIEW Block Diagram

|

NI-DAQmx Function Call

---|---
| Call a sleep or wait function to suspend execution for 350 ms.

9. Acquire 1000 points of voltage data using the Analog 1D DBL 1Chan NSamp instance of the DAQmx Read VI.

LabVIEW Block Diagram

|

NI-DAQmx Function Call

---|---
| Call DAQmxReadAnalogF64 with the following parameters:
taskHandle: taskHandle
numSampsPerChan: -1
timeout: 10.0
fillMode: DAQmx_Val_GroupByChannel
readArray: data
arraySizeInSamples: 1000
sampsPerChanRead: &read
reserved: NULL

10. Compute the mean of the 1000 voltage values that you acquired.
11. Compare the resulting average to the upper and lower limits listed in Table 3. If the result is between the upper and lower limits, the SCXI-1104/C passes the test.
12. Clear the acquisition using the DAQmx Clear Task VI.

LabVIEW Block Diagram

|

NI-DAQmx Function Call

---|---
| Call DAQmxClearTask with the following parameter:
taskHandle: taskHandle

13. Repeat steps 4 through 12 for the remaining channels.
14. Repeat steps 3 through 13 for all test points in Tables 3.

You have finished verifying the analog input accuracy of the SCXI-1104/C.

Adjustment Procedure

The adjustment procedure adjusts the gain and offset calibration constants on the SCXI-1104/C. Complete the Verification Procedure prior to the adjustment procedure to determine the pre-calibration accuracy and whether adjustments are necessary.

Complete the following steps to adjust the gain and offset of the SCXI-1104/C:

1. Connect the calibrator output to pins CH- and CH+ for all channels. Refer to the SCXI-1300/1301 Terminal Block Installation Guide for connection instructions. If you are not using the recommended SCXI-1300, refer to Table 4 for the front signal pin assignments of the SCXI-1104/C. If the calibration signal source is floating, connect CH- to the SCXI chassis ground using the ground lug available on the SCXI terminal block.
2. Connect the DMM to MCH0+ and MCH0- (pin 3 and 4) on the rear connector. Refer to Table 5 for the rear signal pin assignments of the SCXI-1104/C.

          Note   You can access these pins using a 50-pin cable connected to an SCXI-1349.

3. Start an external calibration session using the DAQmx Initialize External Calibration VI.

          Note   Throughout the adjustment procedure, refer to the function call parameters for the LabVIEW input values.

LabVIEW Block Diagram

|

NI-DAQmx Function Call

---|---
| Call DAQmxInitExtCal with the following parameters:
deviceName: “SC1Mod1”
password: “NI”
calHandle: &calHandle

4. Set the SCXI-1104/C to a physical channel using the DAQmx Setup SCXI Calibration VI.

LabVIEW Block Diagram

|

NI-DAQmx Function Call

---|---
| Call DAQmxSetup1104Cal with the following parameters:
calHandle: calHandle
channel: “SC1Mod1/aiX”††Where X refers to the channel you are calibrating.

5. Set the calibrator to the desired voltage. Refer to Table 2 for appropriate voltage set points.

Table 2. SCXI-1104/C Voltage Set Points

Gain

| Set Points (V)
---|---
0.1| -41.80000| 0.0000|

41.8000

6. Wait for 350 ms of settling time to elapse and then record the measured output from the DMM.
7. Adjust the external calibration constants using the DAQmx Adjust SCXI Calibration VI.

LabVIEW Block Diagram

|

NI-DAQmx Function Call

---|---
| Call DAQmxAdjust1104Cal with the following parameters:
calHandle: calHandle
refVoltage: (calibrator output voltage) float64
measOutput: (voltage measured by DMM) float64

8. Repeat steps 5 through 7 for the voltage test points in Table 2.
9. Commit the calibration changes you made in the session using the DAQmx Close External Calibration VI. The data is written to the hardware in this step.

calHandle: calHandle
action: DAQmx_Val_Action_Commit

10. Repeat steps 1 through 9 for the remaining channels.

You have finished adjusting the gain and offset of the SCXI-1104/C.

Verifying Adjusted Values

After calibrating the SCXI-1104/C, NI recommends that you verify the analog input operation by repeating the steps listed in the Verification Procedure to ensure that the SCXI-1104/C is operating within its test limits.

Test Limits

Refer to the SCXI-1104/C User Manual for the specifications of the SCXI-1104/C.

Gain and Offset

Table 3 contains the test limits to use when verifying and adjusting the gain and offset of the SCXI-1104/C. If the SCXI-1104/C was calibrated within the last year, the test point value should fall between the Lower Limit and Upper Limit values found in Table 3.

          Note   The values in Table 3 do not include DAQ device errors.

Table 3. SCXI-1104/C Test Limits

Gain

| Test Point (V)| Upper Limit (V)| Lower Limit (V)
---|---|---|---
0.1| 41.800000| 41.823536|

41.776464

0.000000

| 0.006816| -0.006816
-41.800000| -41.776464|

-41.823536

SCXI-1104/C Front and Rear Panel Diagrams

Table 4 shows the pin assignments for the SCXI-1104/C front panel connector. Table 5 shows the pin assignments for the SCXI-1104/C rear signal connector.

Table 4. Front Signal Pin Assignments

Front Connector Diagram

| Pin Number| Column A| Column B| Column C
---|---|---|---|---

NC—No Connection
RSVD—Reserved

| 32| CH GND| CH 0-|

CH 0+

31

| NC| CH 1-| CH 1+
30| NC| CH 2-|

CH 2+

29

| NC| CH 3-| CH 3+
28| NC| CH 4-|

CH 4+

27

| NC| CH 5-| CH 5+
26| NC| CH 6-|

CH 6+

25

| NC| CH 7-| CH 7+
24| CH GND| CH 8-|

CH 8+

23

| NC| CH 9-| CH 9+
22| NC| CH 10-|

CH 10+

21

| NC| CH 11-| CH 11+
20| NC| CH 12-|

CH 12+

19

| NC| CH 13-| CH 13+
18| NC| CH 14-|

CH 14+

17

| NC| CH 15-| CH 15+
16| CH GND| CH 16-|

CH 16+

15

| NC| CH 17-| CH 17+
14| NC| CH 18-|

CH 18+

13

| NC| CH 19-| CH 19+
12| NC| CH 20-|

CH 20+

11

| NC| CH 21-| CH 21+
10| NC| CH 22-|

CH 22+

9

| NC| CH 23-| CH 23+
8| NC| CH 24-|

CH 24+

7

| NC| CH 25-| CH 25+
6| NC| CH 26-|

CH 26+

5

| CH GND| CH 27-| CH 27+
4| RSVD| CH 28-|

CH 28+

3

| RSVD| CH 29-| CH 29+
2| CH GND| CH 30-|

CH 30+

1

| +5 V| CH 31-|

CH 31+

Table 5. Rear Signal Pin Assignments

Rear Connector Diagram| Signal Name| Pin Number| Pin Number| Signal Name
---|---|---|---|---

NC—No Connection

RSVD—Reserved

| AO GND| 1| 2| AO GND
MCH 0+| 3| 4| MCH 0-
NC| 5| 6| NC
NC| 7| 8| NC
NC| 9| 10| NC
NC| 11| 12| NC
NC| 13| 14| NC
NC| 15| 16| NC
NC| 17| 18| NC
OUT REF| 19| 20| NC
NC| 21| 22| NC
NC| 23| 24| D GND
SER DAT IN| 25| 26| SER DAT OUT
DAQ D/A| 27| 28| NC
SLOT 0 SEL| 29| 30| NC
D GND| 31| 32| NC
NC| 33| 34| NC
NC| 35| 36| SCANCLK
SER CLK| 37| 38| NC
NC| 39| 40| NC
NC| 41| 42| NC
RSVD| 43| 44| NC
NC| 45| 46| RSVD
NC| 47| 48| NC
NC| 49| 50| NC

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