National Instruments SCB-68 Attenuating Voltage

Chapter 5 Adding Components forSpecial Functions

SCB-68 Shielded Connector Block User Manual 5-18 ni.com

Adding Components

Caution Do not exceed ±10V at the analog inputs. NI is not liable for any device damage

or personal injury resulting from improper connections.

You can build a one-resistor circuit for measuring current at the

single-ended or differential inputs of the SCB-68.

Single-Ended Inputs

To build a one-resistor circuit that measures current at the single-ended

analog inputs of the SCB-68, add the resistor to position B or D depending

on the channel being used. Leave the jumpers in place for channel positions

F and G, respectively. Calculate the current according to Equation5-9

or 5-10.

(5-9)

(5-10)

Differential Inputs

To build a one-resistor circuit that measures current at the differential

inputs of the SCB-68, add the resistor to position E for each differential

channel pair that is used. Leave the jumpers in place for positions F and G.

Calculate the current according to Equation5-11:

(5-11)

Attenuating Voltage

This section describes how to add components for attenuating, or

decreasing the amplitude of, a voltage signal. Transducers can output more

than 10 VDC per channel, but DAQ devices cannot read more than 10 VDC

per input channel. Therefore, you must attenuate output signals from the

transducer to fit within the DAQ device specifications. Figure 5-19 shows

how to use a voltage divider to attenuate the output signal of the transducer.

IVm

RB

------=

IVm

RE

------=

IVm

RE

------=

Contents

Main Page Important Information Warranty Copyright Trademarks Patents Compliance FFCC/Canada Radio Frequency Interference Compliance Determining FCC Class FCC/DOC Warnings Class A Compliance to EU Directives Contents Chapter 4 Using Thermocouples Chapter 5 Adding Components for Special Functions Page About This Manual Conventions Page Introduction What You Need to Get Started Quick Reference Label Page Table 1-1. Device-Specific Hardware Configuration (Continued) Installing Cables Using 68-Pin Cables Using 100-Pin Cables Page Figure 1-4. SCB-68 E Series I/O Connector Pinout (Full) Figure 1-5. SCB-68 E Series I/O Connector Pinout (Extended AI) Figure 1-6. SCB-68 E Series I/O Connector Pinout (Extended Digital) Configuring the SCB-68 Safety Information Page Page Parts Locator and Wiring Guide Figure 2-1. SCB-68 Printed Circuit Diagram SCB-68 Switch Configuration Page Page Connecting Signals Connecting Analog Input Signals Input Modes Figure 3-1. Summary of AI Connections Using Bias Resistors Nonreferenced or Floating Signal Sources Ground-Referenced Signal Sources Differential Connection Considerations (DIFF Input Mode) Differential Connections for Ground-Referenced Signal Sources i Figure 3-2. Differential Input Connections for Ground-Referenced Signals Differential Connections for Nonreferenced or Floating Signal Sources Using Bias Resistors Single-Ended Connection Considerations Single-Ended Connections for Floating Signal Sources (RSE Input Mode) Single-Ended Connections for Grounded Signal Sources (NRSE Input Mode) Connecting Analog Output Signals Connecting Digital Signals Connecting Timing Signals Noise Considerations Page Using Thermocouples Switch Settings and Temperature Sensor Configuration Special Considerations Adding Components for Special Functions Channel Pad Configurations Conditioning Analog Input Channels Conditioning Analog Output Channels Figure 5-3. Analog Output Channel Configuration Diagram for DAC0OUT Conditioning PFI0/TRIG1 Figure 5-5. Digital Input Channel Configuration Diagram for PFI0/TRIG1 Figure 5-4. Digital Input Channel Configuration Diagram Accuracy and Resolution Considerations Open Thermocouple Detection Differential Open Thermocouple Detection Single-Ended Open Thermocouple Detection Sources of Error Lowpass Filtering Page Page One-Pole Lowpass RC Filter Selecting Components Single-Ended Lowpass Filter Differential Lowpass Filter Analog Output and Digital Input Lowpass Filtering Lowpass Filtering Applications Noise Filtering Antialiasing Filtering Special Consideration for Analog Input Channels Special Consideration for Analog Output Signals Special Consideration for Digital Trigger Input Signals Measuring a 4 to 20 mA Current Selecting a Resistor Attenuating Voltage Page Selecting Components Accuracy Considerations Single-Ended Input Attenuators Differential Input Attenuators Analog Output and Digital Input Attenuators Special Considerations for Analog Input Special Considerations for Analog Output Special Considerations for Digital Inputs A Specifications Analog Input Power Requirement Fuse Physical Maximum Working Voltage Environmental Safety Electromagnetic Compatibility CE Compliance Page Figure B-1. ESeries Device s SCB-68 Shielded Connector Block User Manual B-2 ni.com E SERIES DEVICES NI 670 Figure B-2. NI670X Devices National Instruments Corporation B-3 SCB-68 Shielded Connector Block User Manual DEVICES NI 671 /673 Figure B-3. NI671X/673X Devices SCB-68 Shielded Connector Block User Manual B-4 ni.com Figure B-4. S Series Devices S SERIES DEVICES NI 660 Figure B-5. NI660X Devices X S5 X NI 653 Figure B-6. NI653X Devices National Instruments Corporation B-7 SCB-68 Shielded Connector Block User Manual DEVICES Figure B-7. NI7811R/7831R Devices NI 7811R/7831R DEVICES C Fuse and Power D SCB-68 Circuit Diagrams Figure D-1. +5 V Power Supply This appendix contains illustrations of circuit diagrams for the SCB-68. Figure D-2. Cold-Junction Compensation Circuitry Figure D-3. Digital Trigger Circuitry Figure D-4. Analog Output Circuitry E Soldering and Desoldering on the SCB-68 Page F Technical Support and Professional Services Page Glossary Numbers/Symbols A C D Page I L M N O P R S T U V W Index Numbers A B C Page D E F G I L M N O P Q R S T V