SCXI 8-Channel Isolated Analog Input SCXI 8-Channel Isolated Analog Input Modules NI SCXI-1125, NI SCXI-1120, NI SCXI-1120D • 8 channels • 333 kS/s maximum sampling rate • Gain and lowpass filter settings per channel • Up to 300 Vrms working isolation per channel • Signal inputs from ±2.5 mV to ±1000 VDC with TBX-1316 • NI-DAQ driver software simplifies configuration, measurement and scaling SCXI-1125 • Programmable gain and filter settings • 300 Vrms working isolation per channel, SCXI-1120, SCXI 1120D • Jumper selectable filter per channel • 4 Hz and 10 kHz filter (SCXI-1120) • 4.5 kHz and 22.5 kHz (SCXI-1120D) • 250 Vrms working isolation per channel Operating Systems • Windows 2000/NT/XP Recommended Software • LabVIEW • LabWindows/CVI • Measurement Studio • VI Logger Driver Software • NI-DAQ 7 Calibration Certificate Included Data Acquisition and Signal Conditioning See page 21. Overview SCXI-1120, SCXI-1120D The National Instruments SCXI-1125, SCXI-1120, and SCXI-1120D are 8-channel isolated analog input modules. These modules share a common architecture, providing 250 to 300 Vrms of working isolation and lowpass filtering for each analog input channel. This architecture is ideal for amplification and isolation of millivolt, volt, 0 to 20 mA, 4 to 20 mA, and thermocouple signals. Each module can multiplex these eight channels into a single channel of the DAQ device, and you can add modules to increase channel count. These modules also offer parallel mode operation for increased scanning rates. The analog inputs of the NI-1120/D consist of eight isolation amplifiers. You can configure each amplifier using jumpers for input ranges from ±2.5 mV to ±5 V (SCXI-1120) or ±5 mV to ±10 V (SCXI-1120D). With the SCXI-1327 high-voltage attenuator terminal block, the input range is extended to ±250 V. With the TBX-1316, the input range is extended to ±1000 VDC (680 Vrms). Each channel also includes a lowpass filter that is jumper configurable for 4 Hz or 10 kHz (SCXI-1120), or for 4.5 or 22.5 kHz (SCXI-1120D). Each channel is individually isolated with a working common-mode voltage of 250 Vrms between channels or channel to earth. In addition, the SCXI-1120 and SCXI-1120D are CE certified as double insulated, Category II, for 250 Vrms of operational isolation. Analog Input SCXI-1125 The analog inputs of the NI SCXI-1125 consist of eight programmable isolation amplifiers. You can program each channel independently for input ranges from ±2.5 mV to ±5 V. With the SCXI-1313 high-voltage attenuator terminal block, the input range is extended to ±300 V. With the TBX-1316, the input range is extended to ±1000 VDC (680 Vrms). Each channel also includes a programmatic lowpass filter that you can configure for 4 Hz or 10 kHz. With the SCXI-1125 you can perform random scanning meaning you can select only the channels from which you want to acquire data as well as scan channels in any order. Each channel is individually isolated with a working common-mode voltage of 300 Vrms between channels or channel to earth. In addition, the SCXI-1125 is CE certified as double insulated, Category II, for 300 Vrms of operational isolation. Cold-Junction Compensation Each of these modules can read the cold-junction sensor from the SCXI-1320, SCXI-1321, SCXI-1327, SCXI-1328, and TBX-1328 terminal blocks. The SCXI-1125 can scan the sensor along with other channels, but the SCXI-1120/D must read the cold-junction sensor as a separate analog input operation. This is commonly done once before the start of a continuous acquisition. Module SCXI-1125 SCXI-1120 SCXI-1120D ±2.5 mV ✓ ✓ – ±5 mV to ±5 V ✓ ✓ ✓ *Using attenuating terminal block. Table 1. Module Compatibility 296 National Instruments • Tel: (800) 433-3488 • Fax: (512) 683-9300 • [email protected] • ni.com ±10 V – – ✓ ±1000 V ✓* ✓ ✓ 0 to 20 mA ✓ ✓ ✓ Thermocouple ✓ ✓ ✓ SCXI 8-Channel Isolated Analog Input Modules CH O+ CH O– Buffer MCHO 1120 Series Only Analog Multiplexer Rear Signal Connector Lowpass Filter Front Signal Connector CH 7+ CH 7– Scan Clock MCH7 Jumper Multiplexer Control Gain Select Lowpass Filter Analog Bus Switch Lowpass Filter To Analog Bus SCXIbus Connector Input Channel 0 Lowpass Filter Input Channel 7 SCXI 8-Channel Isolated Analog Input Isolation Barrier Gain Select Digital Interface and Control MTEMP Figure 1. SCXI-1125, SCXI-1120, and SCXI-1120D Block Diagram Terminal Block Type CJ Sensor Compatible Modules Cabling Special Functions Page 777687-13 ✓ SCXI-1125 – 777687-20 ✓ – 329 SCXI-1327 777687-27 SCXI-1125 SCXI-1120 SCXI-1120D Programmable 100:1 attenuator IC Sensor for CJC 328 SCXI-1320 – 100:1 attenuator 329 SCXI-1328 777687-28 ✓ – 777687-38 ✓ – Isothermal construction Prewired ground referencing For current inputs 329 SCXI-1338 SCXI-13051 777687-05 – – AC coupling 328 TBX-1316 777207-16 331 777207-28 SH32-32-A (183230-01) SH32-32-A (183230-01) 200:1 attenuator TBX-1328 Screw terminals Front-mounting Screw terminals Front-mounting Screw terminals Front-mounting Screw terminals Front-mounting Screw terminals Front-mounting BNC connectors Front-mounting Screw terminals DIN-rail mount Screw terminals DIN-rail mount 331 TBX-1329 777207-29 SCXI-1330 777687-30 DIN-rail mount Isothermal construction Prewired ground referencing DIN-rail mount AC coupling Low-cost connector and shell assembly 1The Screw terminals DIN-rail mount Solder pins Front-mounting ✓ ✓ – SH32-32-A (183230-01) – – 330 Data Acquisition and Signal Conditioning Part Number SCXI-1313 331 329 SCXI-1305 is not intended for high-voltage (>42 V) usage. Table 2. Terminal block options for SCXI-1125, SCXI-1120, and SCXI-1120D. Calibration The SCXI-1125 contains calibration hardware to null out error sources. With programmable offset calibration, software-programmable analog switches ground the inputs of each of the instrumentation amplifiers for offset error calibration. An onboard EEPROM stores the calibration constants for each channel for each input range in a user-defined area. The EEPROM also stores a set of factory calibration constants in permanent memory, and cannot be modified. NI-DAQ driver software transparently uses the calibration constants to correct for gain and offset errors. Ordering Information NI SCXI-1125 ................................................................776572-25 NI SCXI-1120 ................................................................776572-20 NI SCXI-1120D..........................................................776572-20D Accessories SCXI current resistors (4-pack) ..................................776582-01 For information on extended warranty and value-added services, see page 20. BUY ONLINE! Visit ni.com/info and enter scxi1120, scxi1120d and/or scxi1125. See page 276 to configure your complete system. National Instruments • Tel: (800) 433-3488 • Fax: (512) 683-9300 • [email protected] • ni.com 297 SCXI 8-Channel Isolated Analog Input SCXI 8-Channel Isolated Analog Input Modules Specifications Absolute Accuracy Table Module SCXI-1125 Data Acquisition and Signal Conditioning SCXI-1120 Nominal Range* ±1000 Vrms4 ±300 V 3 ±250 V 3 ±100 V3 ±50 V 3 ±25 V 3 ±10 V 3 ±5 V ±2.5 V ±1 V ±500 mV ±250 mV ±100 mV ±50 mV ±25 mV ±20 mV ±10 mV ±5 mV ±2.5 mV ±1000 Vrms4 ±500 Vrms4 ±250 V2 ±100 V2 ±50 V2 ±25 V2 ±10 V2 ±5 V ±2.5 V ±1 V ±500 mV ±250 mV ±100 mV ±50 mV ±25 mV ±20 mV ±10 mV ±5 mV ±2.5 mV Overall Gain* 0.005 0.01 0.02 0.05 0.1 0.2 0.5 1 2 5 10 20 50 100 200 250 500 1000 2000 0.005 0.01 0.02 0.05 0.1 0.2 0.5 1 2 5 10 20 50 100 200 250 500 1000 2000 Percent of Reading* Typical Max 0.3996 1.2489 0.2548 0.6498 0.2548 0.6498 0.2548 0.6498 0.2548 0.6498 0.2548 0.6498 0.2478 0.6478 0.2478 0.6478 0.2478 0.6478 0.2478 0.6478 0.2478 0.6478 0.2478 0.6478 0.2478 0.6478 0.2478 0.6478 0.2478 0.6478 0.2478 0.6478 0.2478 0.6478 0.2478 0.6478 0.2478 0.6478 0.3996 1.2489 0.2548 0.6498 0.2548 0.6498 0.2548 0.6498 0.2548 0.6498 0.2548 0.6498 0.2478 0.6498 0.2478 0.6498 0.2478 0.6498 0.2478 0.6498 0.2478 0.6478 0.2478 0.6478 0.2478 0.6478 0.2478 0.6478 0.2478 0.6478 0.2478 0.6478 0.2478 0.6478 0.2478 0.6478 0.2478 0.6478 Offset* Offset 854 mV 500 mV 250 mV 100 mV 50 mV 25 mV 10 mV 5.0 mV 2.5 mV 1.0 mV 508 µV 258 µV 108 µV 58 µV 33 µV 28 µV 18 µV 13 µV 11 µV 854 mV 337 mV 250 mV 132 mV 65.3 mV 31.9 mV 11.9 mV 11.3 mV 5.13 mV 2.02 mV 1.00 mV 487 µV 193 µV 93.6 µV 45.3 µV 35.6 µV 18.0 µV 13.0 µV 11.1 µV System Noise (peak, 3 sigma)* Single Point Average 4 Hz 10 kHz or FBW 4 Hz 10 kHz or FBW 115 mV 1.62 V 24.5 mV 401 mV 57.7 mV 946 mV 12.7 mV 203 mV 29.9 mV 478 mV 6.26 mV 100 mV 12.0 mV 183 mV 2.51 mV 40.1 mV 5.67 mV 111 mV 1.27 mV 20.3 mV 2.82 mV 47.9 mV 641 uV 10.1 mV 1.05 mV 19.1 mV 238 µV 4.06 mV 528 µV 8.59 mV 122 µV 2.03 mV 254 µV 4.25 mV 59.7 µV 1.01 mV 109 µV 1.68 mV 23.7 µV 403 µV 68.2 µV 882 µV 12.2 µV 202 µV 32.0 µV 474 µV 6.26 µV 101 µV 10.9 µV 180 µV 2.37 µV 40.4 µV 6.20 µV 88.2 µV 1.24 µV 20.3 µV 2.58 µV 47.9 µV 0.593 µV 10.4 µV 2.25 µV 37.1 µV 0.499 µV 8.57 µV 1.27 µV 21.8 µV 0.268 µV 4.69 µV 0.713 µV 14.9 µV 0.170 µV 3.13 µV 0.420 µV 11.2 µV 0.099 µV 2.49 µV 162 mV 1.94 V 38.6 mV 488 mV 86.5 mV 972 mV 18.8 mV 244 mV 37.3 mV 503 mV 9.11 mV 122 mV 15.3 mV 199 mV 3.68 mV 48.4 mV 7.73 mV 98.9 mV 1.79 mV 24.4 mV 4.28 mV 54.6 mV 895 µV 12.3 mV 1.57 mV 26.2 mV 375 µV 4.92 mV 840 µV 10.8 mV 188 µV 2.41 mV 385 µV 5.00 mV 88.7 µV 1.20 mV 157 µV 2.22 mV 36.4 µV 482 µV 80.2 µV 993 µV 18.5 µV 241 µV 45.0 µV 518 µV 9.18 µV 123 µV 15.5 µV 221 µV 3.61 µV 49.3 µV 7.74 µV 108 µV 1.82 µV 24.9 µV 4.21 µV 54.9 µV 0.940 µV 13.3 µV 3.38 µV 50.6 µV 0.788 µV 11.6 µV 1.97 µV 29.3 µV 0.454 µV 7.03 µV 0.962 µV 25.5 µV 0.260 µV 5.58 µV 0.908 µV 22.4 µV 0.314 µV 5.07 µV Temperature Drift Percent of Offset Reading/°C (µV/°C) 0.0034 132 mV 0.0029 44 mV 0.0029 44 mV 0.0029 22 mV 0.0029 11 mV 0.0029 4.4 mV 0.0029 2.2 mV 0.0027 1.12 mV 0.0027 460 µV 0.0027 240 µV 0.0027 130 µV 0.0027 64 µV 0.0027 42 µV 0.0027 31 µV 0.0027 24.4 µV 0.0027 22.2 µV 0.0027 21.1 µV 0.0027 20.9 µV 0.0027 20.3 µV 0.0034 132 mV 0.0029 44 mV 0.0029 44 mV 0.0029 22 mV 0.0029 11 mV 0.0029 4.4 mV 0.0029 2.2 mV 0.0027 1.12 mV 0.0027 460 µV 0.0027 240 µV 0.0027 130 µV 0.0027 64 µV 0.0027 42 µV 0.0027 31 µV 0.0027 24.4 µV 0.0027 22.2 µV 0.0027 21.1 µV 0.0027 20.9 µV 0.0027 20.3 µV *Absolute Accuracy (15 to 35 °C). To calculate the absolute accuracy for the SCXI-1125, SCXI-1120, and SCXI-1120D refer to page 194 or visit ni.com/accuracy Module SCXI-1120D Range* ±1000 Vrms4 ±500 Vrms4 ±200 V2 ±100 V2 ±50 V2 ±20 V2 ±10 V2 ±5 V ±2 V ±1 V ±500 mV ±200 mV ±100 mV ±50 mV ±20 mV ±10 mV ±5 mV Gain* 0.01 0.02 0.05 0.1 0.2 0.5 1 2 5 10 20 50 100 200 500 1000 2000 Percent of Reading* Typical Max 0.3533 0.8832 0.3533 0.8832 0.3533 0.8832 0.3533 0.8832 0.3533 0.8832 0.3533 0.8832 0.3525 0.8812 0.3525 0.8812 0.3525 0.8812 0.3525 0.8812 0.3525 0.8812 0.3525 0.8812 0.3525 0.8812 0.4192 1.0480 0.7800 1.9500 1.3036 3.2590 2.4008 6.0020 Offset* Offset 1.04 V 0.52 V 0.52 V 260 mV 104 mV 52.2 mV 21.0 mV 10.6 mV 5.4 mV 2.28 mV 1.25 mV 726 µV 414 µV 310 µV 258 µV 227 µV 216 µV System Noise (peak, 3 sigma)* Single Point Average 4.5 kHz 22.5 kHz 4.5 kHz 842 mV 4.29 V 206 mV 475 mV 3.15 V 103 mV 179 mV 2.46 V 47.3 mV 104 mV 2.32 V 30.4 mV 71.6 mV 2.23 V 26.1 mV 46.9 mV 1.96 V 21.4 mV 9.65 mV 40.9 mV 2.11 mV 4.38 mV 30.4 mV 1.04 mV 2.13 mV 23.5 mV 483 µV 1.03 mV 22.2 mV 300 µV 677 µV 21.5 mV 256 µV 448 µV 18.9 mV 208 µV 297 µV 13.2 mV 140 µV 271 µV 13.9 mV 140 µV 263 µV 9.50 mV 139 µV 252 µV 4.81 mV 136 µV 243 µV 2.42 mV 131 µV *Absolute Accuracy (15 to 35 °C). To calculate the absolute accuracy for the SCXI-1125, SCXI-1120, and SCXI-1120D refer to page 194 or visit ni.com/accuracy 1V rms refers to sinusoidal waveform; V refers to 2 With SCXI-1327 high-voltage terminal block. 3 With 4 With 298 DC or AC peak. SCXI-1313 high-voltage terminal block. TBX-1316 high-voltage terminal block. National Instruments • Tel: (800) 433-3488 • Fax: (512) 683-9300 • [email protected] • ni.com 22.5 kHz 1.53 V 1.45 V 1.45 V 1.45 V 1.45 V 1.33 V 14.9 mV 14.3 mV 14.3 mV 14.3 mV 14.3 mV 12.8 mV 9.45 mV 9.45 mV 6.35 mV 3.21 mV 1.61 mV Temperature Drift Percent of Offset Reading/°C (V/°C) 0.0059 44 mV 0.0059 44 mV 0.0059 22 mV 0.0059 11 mV 0.0059 4.4 mV 0.0059 2.2 mV 0.0059 900 µV 0.0057 460 µV 0.0057 240 µV 0.0057 108 µV 0.0057 64 µV 0.0057 42 µV 0.0057 28.8 µV 0.0057 24.4 µV 0.0057 22.2 µV 0.0057 20.9 µV 0.0057 20.4 µV SCXI 8-Channel Isolated Analog Input Modules Input Characteristics Dynamic Characteristics Number of channels......................................... 8 differential Input signal ranges Module Signal Ranges SCXI-1125 ±2.5 mV to ±5 V SCXI-1120 ±2.5 mV to ±5 V SCXI-1120D ±5 mV to ±10 V Input signal bandwidth Module SCXI-1125 SCXI-1120 SCXI-1125/1120 SCXI-1125/1120 SCXI-1120D Filter 4 Hz 10 kHz 10 kHz 2, 3 10 kHz 4 4.5 kHz Input coupling................................................... DC (or AC with SCXI-1305 or TBX-1329) Maximum working voltage (without SCXI-1313, 1327, or TBX-1316) Module Signal and Common Mode SCXI-1125 ±300 Vrms SCXI-1120, SCXI-1120D ±250 Vrms Module SCXI-1125 SCXI-1120, SCXI-1120D Powered On ±300 Vrms ±250 Vrms Powered Off ±300 Vrms ±250 Vrms Module SCXI-1125 SCXI-1120 SCXI-1120D Transfer Characteristics Percent of Full Scale Range ±0.02% ±0.04% Offset error ....................................................... See accuracy table Gain error ......................................................... See accuracy table Amplifier Characteristics Normal Powered On >1G >1G >1M Powered Off/Overload 4.5 M 50 k 500 k Input bias current SCXI-1125......................................................... ±100 pA SCXI-1120......................................................... ±80 pA SCXI-1120D ...................................................... ±15 pA NMR (Normal Mode Rejection Ratio) SCXI-1125/1120/1120D ................................... 60 dB CMRR (Common Mode Rejection Ratio) (DC to 60 Hz) Module SCXI-1125 SCXI-1120 SCXI-1120D Filter 4 Hz 10 kHz 4 Hz 10 kHz 4.5 kHz 10 kHz Dimensions....................................................... 3.1 by 17.3 by 20.3 cm (12.2 by 6.8 by 8.0 in) I/O Connector Rear ................................................................. 50-pin male ribbon cable rear connector Front ................................................................. 32-pin male DIN C connector Environment Operating temperature..................................... 0 to 50 ˚C Storage temperature ........................................ -20 to 70 ˚C Relative humidity ............................................. 5 to 90% noncondensing Certification and Compliance SCXI-1120/D..................................................... 250 V, Cat II working voltage SCXI-1125......................................................... 300 V, Cat II working voltage Output range .................................................... ± 5 V Output impedance 1V Multiplexed Mode 100 System noise .................................................... See accuracy table Filter type SCXI-1125......................................................... Third-order Butterworth SCXI-1120, SCXI-1120D ................................... Third order RC Cutoff frequency (-3dB) SCXI-1125......................................................... 4 Hz, 10 kHz (programmable) SCXI-1120......................................................... 4 Hz, 10 kHz (jumper selectable) SCXI-1120D ...................................................... 4.5 kHz, 22.5 kHz (jumper selectable) Stability Module Gain Temperature Coefficient Offset Coefficient SCXI-1125 20 ppm/°C ± 0.2 ± 220/gain) µV/°C SCXI-1120 20 ppm/°C ± .42 ± 250/gain) µV/°C SCXI-1120D 50 ppm/°C ± 20 ± 220/gain) µV/°C Physical CMRR 50 or 60 Hz 160 dB 100 dB 160 dB 100 dB 110 dB 98 dB Module SCXI-1125, SCXI-1120, SCXI-1120D Scan Interval (Per Channel, Any Gain and Filter Setting) Settle to ±0.012 %5 Settle to ±0.006 % 6 Settle to ±0.0015 % 6 3 µs 10 µs 20 µs Data Acquisition and Signal Conditioning Input impedance Module SCXI-1125 SCXI-1120 SCXI-1120D Bandwidth 4 Hz 10 kHz 2.6 kHz 500 Hz 4.5 kHz 4 kHz 3.5 kHz 22.5 kHz 22 kHz 20 kHz 17 kHz 14 kHz Multiplexer performance Overvoltage protection Inputs protected ............................................... CH0..CH7 Nonlinearity Module SCXI-1125 SCXI-1120, SCXI-1120D 22.5 kHz Input Range All ranges All ranges All ranges All ranges ± 250 V to ± 50 mV ± 20 mV to ± 10 mV ± 5 mV ± 250 V to ± 1 V ± 50 mV to ± 20 mV ± 10 V to ± 50 mV ± 10 mV ± 5 mV SCXI 8-Channel Isolated Analog Input Specifications European Compliance Parallel Mode 330 rms refers to sinusoidal waveform; V refers to DC or AC peak. 2 With SCXI-1327 high-voltage terminal block. 3 With SCXI-1313 high-voltage terminal block. 4 With TBX-1316 high-voltage terminal block. 5 Includes effects of AT-MIO-16E-2 with 1 or 2 m SCXI cable assembly. 6 Includes effects of AT-MIO-16X or AT-AI-16XE-10 with 1 or 2 m SCXI cable assembly. EMC EN 61326 Group I Class A, 10m, Table 1 Immunity Safety .............................................................. EN 61010-1 North American Compliance EMC ................................................................. FCC Part 15 Class A using CISPR Safety ............................................................... UL Listed to UL 3111-1 CAN/CSA C22.2 No. 1010.1 Australia & New Zealand Compliance EMC ................................................................. AS/NZS 2064.1/2 (CISPR-11) For a definition of specific terms, please visit ni.com/glossary National Instruments • Tel: (800) 433-3488 • Fax: (512) 683-9300 • [email protected] • ni.com 299 Data Acquisition and Signal Conditioning Multifunction DAQ Accuracy Specifications Multifunction DAQ and SCXI Signal Conditioning Accuracy Specifications Overview Every Measurement Counts There is no room for error in your measurements. From sensor to software, your system must deliver accurate results. NI provides detailed specifications for our products so you do not have to guess how they will perform. Along with traditional data acquisition specifications, our E Series multifunction data acquisition (DAQ) devices and SCXI signal conditioning modules include accuracy tables to assist you in selecting the appropriate hardware for your application. To calculate the accuracy of NI measurement products, visit ni.com/accuracy Absolute Accuracy Absolute accuracy is the specification you use to determine the overall maximum tolerance of your measurement. Absolute accuracy specifications apply only to successfully calibrated DAQ devices and SCXI modules. There are four components of an absolute accuracy specification: • Percent of Reading – is a gain uncertainty factor that is multiplied by the actual input voltage for the measurement. • Offset – is a constant value applied to all measurements. • System Noise – is based on random noise and depends on the number of points averaged for each measurement (includes quantization error for DAQ devices). • Temperature Drift – is based on variations in your ambient temperature. • Input Voltage – the absolute magnitude of the voltage input for this calculation. The fullscale voltage is most commonly used. Based on these components, the formula for calculating absolute accuracy is: Absolute Accuracy = ±[(Input Voltage X % of Reading) + (Offset + System Noise + Temperature Drift)] Absolute Accuracy RTI1 = (Absolute Accuracy Input Voltage) 1RTI = relative to input Temperature drift is already accounted for unless your ambient temperature is outside 15 to 35 °C. For instance, if your ambient temperature is at 45 °C, you must account for 10 °C of drift. This is calculated by: Below is the Absolute Accuracy at Full Scale calculation for the NI PCI-6052E DAQ device after one year using the ±10 V input range while averaging 100 samples of a 10 V input signal. In all the Absolute Accuracy at Full Scale calculations, we assume that the ambient temperature is between 15 and 35 °C. Using the Absolute Accuracy table on the next page, we see that that the calculation for the ±10 V input range for Absolute Accuracy at Full Scale yields 4.747 mV. This calculation is done using the parameters in the same row for one year Absolute Accuracy Reading, Offset and Noise + Quantization, as well as a value of 10 V for the input voltage value. You can then see that the calculation is as follows: Absolute Accuracy = ±[(10 X 0.00037) + 947.0 µV + 87 µV] = ±4.747 mV In many cases, it is helpful to calculate this value relative to the input (RTI). Therefore, you do not have to account for different input ranges at different stages of your system. Absolute Acuracy RTI = (±0.004747/10) = ±0.0475% The following example assumes the same conditions except that the ambient temperature is 40 °C. You can begin with the calculation above and add in the Drift calculation using the % Drift per °C from Table 2 on page 196. Absolute Accuracy = 4.747 mV + ((40 – 35 °C) x 0.000006 /°C X 10 V) = ±5.047 mV Absolute Acuracy RTI = (±0.005047/10) = ±0.0505% Absolute Accuracy for SCXI Modules Below is an example for calculating the absolute accuracy for the NI SCXI-1102 using the ±100 mV input range while averaging 100 samples of a 14 mV input signal. In this calculation, we assume the ambient temperature is between 15 and 35 °C, so Temperature Drift = 0. Using the accuracy table on page 313, you find the following numbers for the calculation: Input Voltage = 0.014 % of Reading Max = 0.02% = 0.0002 Offset = 0.000025 V System Noise = 0.000005 V Absolute Accuracy = ±[(0.014 x 0.0002) + 0.000025 + 0.000005] V = ±32.8 µV Temperature Drift = Temperature Difference x % Drift per °C x Input Voltage Absolute Accuracy for DAQ Devices Absolute Device Accuracy at Full Scale is a calculation of absolute accuracy for DAQ devices for a specific voltage range using the maximum voltage within that range taken one year after calibration, the Accuracy Drift Reading, and the System Noise averaged value. Absolute Accuracy RTI = ±(0.0000328 / 0.014) = ±0.234 % The following example assumes the same conditions, except the ambient temperature is 40 °C. You can begin with the Absolute Accuracy calculation above and add in the Temperature Drift. Absolute Accuracy = 32.8 µV + (0.014 x 0.000005 + 0.000001) x 5 = ±38.15 µV Absolute Accuracy RTI = ±(0.00003815 / 0.014) = ±0.273 % 194 National Instruments • Tel: (800) 433-3488 • Fax: (512) 683-9300 • [email protected] • ni.com Multifunction DAQ and SCXI Signal Conditioning Accuracy Specifications Overview System Noise = Average System Noise from table x (100/number of points) For example, if you are averaging 1,000 points per measurement with the PCI-6052E in the ±10 V (±100 mV for the SCXI-1102) input range, System Noise is determined by: NI PCI-6052E** System Noise= 87.0 0 µV x (100/1000) = 27.5 0 µV NI SCXI-1102 System Noise= 5 µV x SQRT (100/1000) = 1.58 µV **The System Noise specifications assume that dithering is disabled for single-point measurements and enabled for averaged measurements. 1. Convert a typical expected value from the unit of measure to voltage 2. Calculate absolute accuracy for that voltage 3. Convert absolute accuracy from voltage to the unit of measure Note: it is important to use a typical measurement value in this process, because many conversion algorithms are not linearized. You may want to perform conversions for several different values in your probable range of inputs, rather than just the maximum and minimum values. For an example calculation, we want to determine the absolute system accuracy of an NI SCXI-1102 system with a NI PCI-6052E, measuring a J-type thermocouple at 100 °C. 1. A J-type thermocouple at 100 °C generates 5.268 mV (from a standard conversion table or formula) 2. The absolute accuracy for the system at 5.268 mV is ±0.82%. This means the possible voltage reading is anywhere from 5.225 to 5.311 mV. 3. Using the same thermocouple conversion table, these values represent a temperature spread of 99.3 to 100.7 °C. Benchmarks Absolute System Accuracy Absolute System Accuracy represents the end-to-end accuracy including the signal conditioning and DAQ device. Because absolute system accuracy includes components set for different input ranges, it is important to use Absolute Accuracy RTI numbers for each component. Total System Accuracy RTI = ±SQRT [(Module Absolute Accuracy RTI)2 + (DAQ Device Absolute Accuracy RTI)2] The following example calculates the Absolute System Accuracy for the SCXI-1102 module and PCI-6052E DAQ board described in the first examples: Total System Accuracy RTI = ± [(0.00273)2 + (0.000505)2] = ±0.278% The calculations described above represent the maximum error you should receive from any given component in your system, and a method for determining the overall system error. However, you typically have much better accuracy values than what you obtain from these tables. If you need an extremely accurate system, you can perform an end-to-end calibration of your system to reduce all system errors. However, you must calibrate this system with your particular input type over the full range of expected use. Accuracy depends on the quality and precision of your source. We have performed some end-to-end calibrations for some typical configurations and achieved the results in Table 1: To maintain your measurement accuracy, you must calibrate your measurement system at set intervals over time. Data Acquisition and Signal Conditioning Therefore, the absolute system accuracy is ±0.7 °C at 100 °C. See page 21 or visit ni.com/calibration for more information on the importance of calibration on DAQ device accuracy. Multifunction DAQ Accuracy Specifications For both DAQ devices and SCXI modules, you should use the Single-Point System Noise specification from the accuracy tables when you are making single-point measurements. If you are averaging multiple points for each measurement, the value for System Noise changes. The Averaged System Noise in the accuracy tables assumes that you average 100 points per measurement. If you are averaging a different number of points, use the following equation to determine your Noise + Quantization: For a current list of SCXI signal conditioning products with calibration services, please visit ni.com/calibration Units of Measure In many applications, you are measuring some physical phenomenon, such as temperature. To determine the absolute accuracy in terms of your unit of measure, you must perform three steps: National Instruments • Tel: (800) 433-3488 • Fax: (512) 683-9300 • [email protected] • ni.com 195 Multifunction DAQ Accuracy Specifications Multifunction DAQ and SCXI Signal Conditioning Accuracy Specifications Overview Module SCXI-1102 SCXI-1112 SCXI-1125 Empirical Accuracy ±0.25 ˚C at 250 ˚C ±24 mV at 9.5 V ±0.21 ˚C at 300 ˚C ±2.2 mV at 2 V Table 1. Possible Empirical Accuracy with System Calibration Absolute Accuracy Nominal Range (V) Positive FS Negative FS 10.0 -10.0 5.0 -5.0 2.5 -2.5 1.0 -1.0 0.5 -0.5 0.25 -0.25 0.1 -0.1 0.05 -0.05 10.0 0.0 5.0 0.0 2.0 0.0 1.0 0.0 0.5 0.0 0.2 0.0 0.1 0.0 % of Reading 24 Hours 1 Year 0.0354 0.0371 0.0054 0.0071 0.0354 0.0371 0.0354 0.0371 0.0354 0.0371 0.0404 0.0421 0.0454 0.0471 0.0454 0.0471 0.0054 0.0071 0.0354 0.0371 0.0354 0.0371 0.0354 0.0371 0.0404 0.0421 0.0454 0.0471 0.0454 0.0471 Offset Offset (mV) (µV) 947.0 476.0 241.0 99.2 52.1 28.6 14.4 9.7 476.0 241.0 99.2 52.1 28.6 14.4 9.7 System Noise (mV) Single Point Averaged 981.0 87.0 491.0 43.5 245.0 21.7 98.1 8.7 56.2 5.0 32.8 3.0 22.4 2.1 19.9 1.9 491.0 43.5 245.0 21.7 98.1 8.7 56.2 5.0 39.8 3.0 22.4 2.1 19.9 1.9 Data Acquisition and Signal Conditioning Table 2. NI PCI-6052E Analog Input Accuracy Specifications 196 Note: Accuracies are valid for measurements following an internal (self) E Series calibration. Averaged numbers assume averaging of 100 single-channel readings. Measurement accuracies are listed for operational temperatures within ±1 °C of internal calibration temperature and ±10 °C of external or factory-calibration temperature. One-year calibration interval recommended. The absolute accuracy at full scale calculations were performed for a maximum range input voltage (for example, 10 V for the ±10 V range) after one year, assuming 100 point averaging of data. National Instruments • Tel: (800) 433-3488 • Fax: (512) 683-9300 • [email protected] • ni.com Relative Accuracy Temp Drift (%/°C) 0.0006 0.0001 0.0006 0.0006 0.0006 0.0006 0.0006 0.0006 0.0001 0.0006 0.0006 0.0006 0.0006 0.0006 0.0006 Absolute Accuracy atatFull FullScale Scale((((mV (mV) 4.747 0.876 1.190 0.479 0.243 0.137 0.064 0.035 1.232 2.119 0.850 0.428 0.242 0.111 0.059 Resolution (µV) Single Point Averaged 1145.0 115.0 573.0 57.3 286.0 28.6 115.0 11.5 66.3 6.6 39.2 3.9 27.7 2.8 25.3 2.5 573.0 57.3 286.0 28.6 115.0 11.5 66.3 6.6 48.2 3.9 27.7 2.8 25.3 2.5