Agilent 34970A/34972A Data Acquisition / Switch Unit

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Chapter 5 Theory of Operation Power Supplies The 5 volt earth referenced supply (+5V_ER) is produced by rectifier CR101, CR102, CR103, CR104, and regulator U101. This supply is earth referenced by the screw which mounts the PC board to the instrument chassis. The unswitched +5V_ER supplies U305, U303, U320, and U302. The rear-panel interfaces (GPIB, RS-232, Alarms, and external triggers) are powered from the switched +5V_BP supply to ensure that when power is turned off no voltages are present at the interfaces. The +5V_ER supply is switched by Q101A and Q101B to create the +5V_BP (backplane) and fan power supplies. Undervoltage sensor U102 provides the earth reference controller reset at initial power on. 136
Chapter 5 Theory of Operation Front Panel Front Panel Unless otherwise noted, components in this discussion are located on the A2 circuit assembly (34970-66502). The front-panel circuits consist of vacuum fluorescent display control, display high voltage drivers, and keyboard scanning. Communication between the front panel and floating logic circuits is accomplished 4 through a 2-wire bi-directional serial interface. The front-panel logic operates from -13 volts (logic 1) and -18 volts (logic 0). The two serial communication signals are level shifted by comparator U6 from the floating logic 0 V to 5 V levels to the -18 V to -13 V levels present on the front panel assembly. The front panel logic high supply (-13 volts) is produced from the -18 volt supply by voltage regulator U7. Display anode and grid voltages are +18 volts for an on segment and -18 volts for an off segment. The -11 V cathode bias for the display is provided by the main pc boards filament winding center tap bias circuit A1CR108, A1R106, and A1C106. Keyboard scanning is accomplished through a conventional scanned rowcolumn key matrix. Keys are scanned by outputting data at microprocessor U1 port pins P0.0 through P0.4 to poll each key column for a key press. Column read-back data are read by the microprocessor at port pins P2.0 through P2.3 for decoding and communication to the floating logic circuits. Rotary knob quadrature inputs are read directly by the microprocessor port pins P2.6 and P2.7. The standby power switch, S19, provides a low true signal to main controller A1U205. In turn, A1U205 takes actions that either place the instrument in the “standby mode” or “on” mode. In “standby”, both the filament supply to the front panel and the +5V_BP supply to the backplane, rear panel interfaces, and fan are turned off. 5 137
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Agilent 34970A/34972A Data Acquisit
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Safety Notices A CAUTION notice den
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Note: Unless otherwise indicated, t
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The Front-Panel Menu at a Glance Se
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The 34970A Rear Panel at a Glance 4
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The Plug-In Modules at a Glance For
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34907A Multifunction Module • Two
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Contents Chapter 1 Specifications D
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Contents Gain Adjustment 92 -10 VDC
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Contents Plug-In Module Disassembly
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1 1 • DC, Resistance, and Tempera
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DC Measurement and Operating Charac
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AC Measurement and Operating Charac
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Chapter 1 Specifications System Spe
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Chapter 1 Specifications Module Spe
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Typical AC Performance Graphs 34905
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Product and Module Dimensions Chapt
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Chapter 1 Specifications To Calcula
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Chapter 1 Specifications Interpreti
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Chapter 1 Specifications Configurin
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2 2 Quick Start
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Chapter 2 Quick Start To Prepare th
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Chapter 2 Quick Start To Connect Wi
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Chapter 2 Quick Start To Configure
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Chapter 2 Quick Start To Close a Ch
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Chapter 2 Quick Start If the Instru
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Chapter 2 Quick Start To Rack Mount
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3 3 Front-Panel Overview
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Chapter 3 Front-Panel Overview Fron
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Chapter 3 Front-Panel Overview Fron
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Chapter 3 Front-Panel Overview To S
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Chapter 3 Front-Panel Overview To P
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Chapter 3 Front-Panel Overview To R
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Chapter 3 Front-Panel Overview To W
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Chapter 3 Front-Panel Overview To O
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4 4 Calibration Procedures
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Chapter 4 Calibration Procedures Ag
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Chapter 4 Calibration Procedures Re
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Chapter 4 Calibration Procedures Ca
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Chapter 4 Calibration Procedures Ca
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Chapter 4 Calibration Procedures Te
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Chapter 4 Calibration Procedures Pe
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Chapter 6 Service Disassembly Addit
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Chapter 6 Service Disassembly Recyc
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Chapter 6 Service Disassembly Part
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Chapter 6 Service Parts List for 34
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Agilent 34970A/34972A Data Acquisition / Switch Unit

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