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Unformatted text preview: , use bias resistors if the DAQ device is in DIFF input mode. For a single-ended configuration, use RSE input mode. For more information on field wiring considerations, refer to the NI Developer Zone tutorial, Field Wiring and Noise Considerations for Analog Signals, located at ni.com/zone. Cold-junction compensation (CJC) with the SCB-68 is accurate only if the temperature sensor reading is close to the actual temperature of the screw terminals. When you read thermocouple measurements, keep the SCB-68 away from drafts or other temperature gradients, such as those caused by heaters, radiators, fans, and very warm equipment. To minimize temperature gradients, keep the cover of the SCB-68 closed and add custom insulation, such as foam tape, to the SCB-68. Switch Settings and Temperature Sensor Configuration
To accommodate thermocouples with DAQ devices, the SCB-68 has a temperature sensor for CJC. To power the temperature sensor, set switches S1, S2, and S3 as shown in Figures 4-1 and 4-2. Notice that this configuration also powers on the signal conditioning accessory power. Signal conditioning accessories include temperature sensors and signal conditioning circuitry. For single-ended operation, connect referenced single-ended analog channel 0 to the temperature sensor by switching S5 to the up position. The signal is referenced to AIGND. Set the switches as shown in Figure 4-1. SCB-68 Shielded Connector Block User Manual 4-2 ni.com Chapter 4 Using Thermocouples Temperature Sensor S5 S4 S3 Signal Conditioning Circuitry Power (On) S1 S2 Figure 4-1. Single-Ended Switch Configuration For differential operation, connect differential analog channel 0 to the temperature sensor by switching S5 and S4 to the up position, as shown in Figure 4-2.
Temperature Sensor S5 S4 S3 Signal Conditioning Circuitry Power (On) S1 S2 Figure 4-2. Differential Switch Configuration Special Considerations
To connect a high-value resistor between the positive input and +5V, refer to the Accuracy and Resolution Considerations section of Chapter 5, Adding Components for Special Functions. To reduce noise by connecting a lowpass filter to the analog inputs of the SCB-68, refer to the Lowpass Filtering section of Chapter 5, Adding Components for Special Functions. National Instruments Corporation 4-3 SCB-68 Shielded Connector Block User Manual Adding Components for Special Functions 5 This chapter describes how to condition signals by adding components to the open component locations of the SCB-68. To add components to these locations, the DAQ device must support switch configurations 2, 3, or 4 in Table 2-1, Switch Configurations and Affected Signals.
Caution Add components at your own risk. The following signal conditioning applications are described in this chapter: Analog input Open thermocouple detection Lowpass filtering Measuring 420 mA current Voltage attenuation Lowpass smoothing filter Voltage attenuation Lowpass digital filter Voltage attenuation Analog output Digital input In addition to the applications described in this chapter, many other types of signal conditioning can be built using the component pads and the general-purpose breadboard area of the SCB-68. Refer to Appendix E, Soldering and Desoldering on the SCB-68, for more information about adding components and for soldering and desoldering instructions. After building one of the applications described in this chapter or your own custom circuitry, refer to the Configuring the SCB-68 section of Chapter 1, Introduction, for instructions about how to configure the SCB-68 in MAX. National Instruments Corporation 5-1 SCB-68 Shielded Connector Block User Manual Chapter 5 Adding Components for Special Functions You can create virtual channels in MAX to map your voltage ranges to the type of transducer that you are using or to create a custom scale. Channel Pad Configurations
When you use the SCB-68 with a 68-pin or 100-pin DAQ device, you can use the component pads on the SCB-68 to condition 16 AI channels, two AO channels, and PFI0/TRIG1. Conditioning Analog Input Channels
Figure 5-1 illustrates the AI channel configuration. ACH<i> and ACH<i+8> can be used as either a differential channel pair or as two single-ended channels. Table 5-1 correlates the component labels of the SCB-68 to component locations AG for differential channels 07. In the component names in Table 5-1, R denotes a resistor, and C denotes a capacitor. Component locations labeled RCX provide sockets for two components, a resistor and a capacitor, to be connected in parallel.
+5V ACH<i> (A) (B) (E) (C) (D) (G) (F) AIGND ACH<i+8> Figure 5-1. Analog Input Channel Configuration Diagram for ACH<i> and ACH<i+8> Table 5-1. Component Location for Analog Input Channels in DIFF Input Mode Channel ACH0 ACH1 ACH2 ACH3 A R22 R24 R26 R28 B RC12 RC14 RC14 RC18 C RC13 RC15 RC17 RC19 D R23 R25 R27 R29 E RC4 RC5 RC6 RC7 F R4 R6 R8 R10 G R5 R7 R9 R11 SCB-68 Shielded Connector Block User Manual 5-2 ni.com Chapter 5 Adding Components for Special Func...
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This note was uploaded on 05/19/2012 for the course ELEN 3030 taught by Professor Joshi during the Spring '12 term at Marquette.
- Spring '12