INSTALLATION GUIDE SCXI™-1322 HIGH-VOLTAGE TERMINAL BLOCK This guide describes how to use and install the SCXI-1322 terminal block with the SCXI-1122 module. Introduction The SCXI-1322 terminal block consists of a shielded board with 48 screw terminals for easy connection to the SCXI-1122 input connector. Sixteen pairs of screw terminals connect to the SCXI-1122 module inputs. The remaining seven pairs of screw terminals are for the module excitation channels. What You Need to Get Started To set up and use your SCXI-1322 terminal block, you need the following items: ❑ SCXI-1322 terminal block ❑ SCXI-1322 High-Voltage Terminal Block Installation Guide ❑ SCXI chassis ❑ SCXI-1122 module ❑ Number 1 and 2 Phillips-head screwdrivers ❑ 1/8 in. flathead screwdriver ❑ Long-nose pliers ❑ Wire cutter ❑ Wire insulation stripper CVI™, LabVIEW™, and National Instruments™, ni.com™, NI-DAQ™, and SCXI™ are trademarks of National Instruments Corporation. Product and company names are trademarks or trade names of their respective companies. 321925B-01 © Copyright 1993, 1999 National Instruments Corp. All rights reserved. November 1999 Conventions The following conventions are used in this guide: This icon denotes a note, which alerts you to important information. This icon denotes a caution, which advises you of precautions to take to avoid injury, data loss, or a system crash. italic Italic text denotes variables, emphasis, a cross reference, or an introduction to a key concept. This font 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, and code excerpts. Safety Information Cautions Do not operate the device in an explosive atmosphere or where there may be flammable gases or fumes. Keep away from live circuits. Do not remove equipment covers or shields unless you are trained to do so. If signal wires are connected to the device, hazardous voltages may exist even when the equipment is turned off. To avoid a shock hazard, do not perform procedures involving cover or shield removal unless you are qualified to do so and disconnect all field power prior to removing covers or shields. Equipment described in this document must be used in an Installation Category II environment per IEC 664. This category requires local level supply mains-connected installation. Do not operate damaged equipment. The safety protection features built into this device can become impaired if the device becomes damaged in any way. If the device is damaged, turn the device off and do not use until service-trained personnel can check its safety. If necessary, return the device to National Instruments for service and repair to ensure that its safety is not compromised. Do not operate this equipment in a manner that contradicts the information specified in this document. Misuse of this equipment could result in a shock hazard. Terminals are for use only with equipment that has no accessible live parts. SCXI-1322 Installation Guide 2 www.ni.com Do not substitute parts or modify equipment. Because of the danger of introducing additional hazards, do not install unauthorized parts or modify the device. Return the device to National Instruments for service and repair to ensure that its safety features are not compromised. When using the device with high common-mode voltages, you must insulate your signal wires for the highest input voltage. National Instruments is not liable for any damages or injuries resulting from inadequate signal wire insulation. Use only 26-14 AWG wire with a voltage rating of 300 V and 60 °C for signals that may come in contact with 250 V; use only 600 V and 60 °C wire for signals that may come in contact with 480 V. When connecting or disconnecting signal lines to the SCXI terminal block screw terminals, make sure the lines are powered off. Potential differences between the lines and the SCXI ground create a shock hazard while you connect the lines. Connections, including power signals to ground and vice versa, that exceed any of the maximum signal ratings on the SCXI device can create a shock or fire hazard or can damage any or all of the boards connected to the SCXI chassis, the host computer, and the SCXI device. National Instruments is not liable for any damages or injuries resulting from incorrect signal connections. If high voltages (≥30 Vrms and 42.4 Vpeak or 60 VDC) are present, you must connect a safety earth ground wire to the terminal block safety ground solder lug, shown in Figure 1. This complies with safety agency requirements and protects against electric shock when the terminal block is not connected to the chassis. To connect the safety earth ground to the safety ground solder lug, run an earth ground wire in the cable from the signal source to the terminal block. National Instruments is not liable for any damages or injuries resulting from inadequate safety earth ground connections. Do not loosen or re-orient the safety ground solder lug hardware when connecting the safety ground wire; to do so reduces the safety isolation between the high voltage and safety ground. Using the VEX/SENSE+ and the VEX/SENSE– Terminals for Strain-Gauge Excitation Your terminal block has two terminals labeled VEX/SENSE+ and VEX/SENSE–. When resistors R3 and R4 are loaded (factory default), you can use the VEX/SENSE+ and VEX/SENSE– terminals as VEX+ and VEX– terminals, respectively. When you have a heavy load—for example, all 16 channels are connected to 16 120 Ω strain-gauge half-bridges—you should remove resistors R3 and R4 to transform the VEX/SENSE+ and VEX/SENSE– terminals to sense terminals. These terminals must connect to the VEX+ and VEX– leads at the load for remote sensing and therefore compensate for the voltage drop in the excitation leads. © National Instruments Corporation 3 SCXI-1322 Installation Guide It is important to notice that because the SCXI-1122 provides a single voltage excitation channel, you can remotely sense your excitation voltage at a single load location. Therefore, when using multiple loads, you either have to sense in the terminal block (leave R3 and R4 in place) or make sure your loads are located close to each other and remotely sense at the end of the excitation leads. Use a single pair of excitation leads for all the loads, as shown in Figure 1. Use short lengths of large-gauge wire to minimize the voltage drop in each lead. SENSE + VEX + 120 Ω CH+(0) 120 Ω 120 Ω 120 Ω CH+(1) CH+(15) 120 Ω 120 Ω VEX – SENSE – Figure 1. Remote Sensing with Multiple Loads Figure 2 shows a setup where remote sensing is not used. In this case, use a different pair of excitation leads for each load. To minimize the voltage drop in each pair of excitation leads, use large gauge wires to reduce the I * RLEAD drop. VEX + VEX – I 120 Ω 120 Ω CH+(0) 120 Ω I= 120 Ω CH+(1) CH+(15) 120 Ω 3.333 V 240+ 2R LEAD 2R LEAD<< 240Ω 120 Ω R LEAD Figure 2. No Remote Sensing SCXI-1322 Installation Guide 4 www.ni.com Figure 3 shows multiple loads with bad remote sensing. Only the load at which the sense leads connect are correctly regulated. The other loads suffer from the voltage drop in their excitation leads because of current flow. Long Wire VEX + 120 Ω s on ti ec n on dC Ba CH+(0) 120 Ω 120 Ω CH+(1) CH+(2) 120 Ω 120 Ω VEX – SENSE + 120 Ω SENSE – s on ti ec n on C ad B 120 Ω CH+(6) 120 Ω 120 Ω 120 Ω CH+(10) CH+(3) 120 Ω 120 Ω Figure 3. Multiple Loads with Bad Remote Sensing © National Instruments Corporation 5 SCXI-1322 Installation Guide Temperature Sensor Output and Accuracy The SCXI-1322 temperature sensor outputs 1.91 to 0.58 V from 0 to 55 °C and has an accuracy of ±0.5 °C over the 15 to 35 °C range and ±0.9 °C over the 0 to 15 °C and 35 to 55 °C ranges.1 National Instruments software can convert a thermistor voltage to the thermistor temperature for the circuit diagram shown later in this guide. In LabVIEW, you can use the ConvertThermistorReading VI in the Data Acquisition»Signal Conditioning palette. If you are using LabWindows/CVI or NI-DAQ, use the Thermistor_Convert function. The VI takes the output voltage of the temperature sensor, the reference voltage, and the precision resistance and returns the thermistor temperature. Alternatively, you can use the following formulas: T(° C) = TK – 273.15 where TK is the temperature in Kelvin 1 T K = ------------------------------------------------------------3 [ a + b ( ln R T ) + c ( ln R T ) ] a = 1.295361 × 10 – 3 b = 2.343159 × 10 – 4 c = 1.018703 × 10 – 7 RT = resistance of the thermistor in ohms V TEMPOUT R T = 5, 000 -------------------------------------- 2.5 – V TEMPOUT VTEMPOUT = output voltage of the temperature sensor [T(°C ) ]9 T ( °F ) = ----------------------- + 3 5 where T(°F) and T(°C) are the temperature readings in degrees Fahrenheit and degrees Celsius, respectively. Note Use an average of a large number of samples to obtain the most accurate reading. Noisy environments require more samples for greater accuracy. 1 Includes the combined effects of the temperature sensor accuracy and the temperature difference between the temperature sensor and any screw terminal. The temperature sensor accuracy includes tolerances in all component values, the effects caused by temperature and loading, and self-heating. SCXI-1322 Installation Guide 6 www.ni.com Signal Connection Note Refer to the Safety Information section before removing equipment covers or connecting or disconnecting any signal wires. When connecting your signals to the SCXI-1322, follow the labeling on the SCXI-1322 for the appropriate module, as indicated in Figure 5. To connect the signal to the terminal block, perform the following steps, referring to Figures 4 and 5 as necessary: 1. Unscrew the top cover screws and remove the cover. 2. Loosen the strain-relief screws and remove the strain-relief bar. 3. Run the signal wires through the strain-relief opening. You can add insulation or padding if necessary. 4. Prepare your signal wire by stripping the insulation no more than 7 mm. 5. 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 shorting and causing a failure. 6. Tighten the screws to a torque of 5–7 in.-lb. 7. Connect safety earth ground to the safety-ground solder lug. Refer to the Safety Information section for connection information. 8. Reinstall the strain-relief bar and tighten the strain-relief screws. 9. Reinstall the top cover and tighten the top cover screws. 10. Connect the terminal block to the module front connector as explained in the Installation section. © National Instruments Corporation 7 SCXI-1322 Installation Guide Figure 4 shows the SCXI-1322 terminal block parts locator diagram. 2 6 7 3 1 4 5 Back View 1 2 Strain-Relief Bar Strain-Relief Screws 3 Front View Safety-Ground Solder Lug 4 5 Mating Connector Thumbscrew 6 7 Top Cover Screws Top Cover Figure 4. SCXI-1322 Parts Locator Diagram Figure 5 shows the SCXI-1322 signal connections. 4 5 6 3 2 2 1 1 2 Solder Lugs Screw Terminals 3 4 Product Name, Assembly Number, and Revision Letter 5 R3 6 R4 Serial Number Figure 5. SCXI-1322 Signal Connections SCXI-1322 Installation Guide 8 www.ni.com Installation To connect the terminal block to the SCXI module front connector, perform the following steps: 1. Connect the module front connector to its mating connector on the terminal block. 2. Tighten the top and bottom thumbscrews on the back of the terminal block to hold it securely in place. Note For accurate cold-junction compensation, place the SCXI chassis away from an extreme temperature differential. Cleaning the Terminal Block Clean the terminal block by brushing off light dust with a soft, nonmetallic brush. Remove other contaminants with deionized water and a stiff nonmetallic brush. The unit must be completely dry and free from contaminants before returning to service. Specifications All specifications are typical at 25 °C unless otherwise specified. Cold-junction sensor Accuracy1 ........................................ 0.65° from 15 to 35 °C 0.85° from 0 to 15 °C and 35 to 55 °C Repeatability ................................... 0.4° from 15 to 35 °C Output ............................................. 1.91 to 0.58 V from 0 to 55 °C Common-mode isolation Terminal to terminal ....................... 250 Vrms Terminal to earth............................. 480 Vrms 1 The temperature sensor accuracy includes tolerances in all component values, effects caused by temperature, loading, self-heating, and temperature gradients. © National Instruments Corporation 9 SCXI-1322 Installation Guide Environment Operating temperature ............................0 to 50 °C Storage temperature ................................–20 to 70 °C Relative humidity ...................................5% to 90% noncondensing Safety Designed in accordance with IEC 61010-1, UL 3111-1, and CAN/CSA C22.2 No. 1010.1 for electrical measuring and test equipment. Approved at altitudes up to 2000 meters. Installation Category II Pollution Degree 2 Temperature Sensor Circuit Diagram The circuit diagram in Figure 6 is optional information that you can use if you want more details about the SCXI-1322 temperature sensor. +5 V 4.7 kΩ 1% 2.5 V LM 4040 2.5 V 0.1% 2 5 kΩ 0.1% 0.1 µF -t o MTEMP + 1 10 µF 5 kΩ at 25o C 2 16 V 1 2 0.1 µF Figure 6. Temperature Sensor Circuit Diagram SCXI-1322 Installation Guide 10 www.ni.com Technical Support Resources NI Web Support To provide you with immediate answers and solutions 24 hours a day, 365 days a year, National Instruments maintains extensive online technical support resources. They are available to you at no cost, are updated daily, and can be found in the Technical Support section of our Web site at www.ni.com/support Worldwide Support National Instruments has offices located around the globe. Many branch offices maintain a Web site to provide information on local services. 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