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HYDRA
Service Manual
ii
2-32. Digital Kernel ............................................................................. 2-10
2-43. Digital I/O ................................................................................... 2-14
2-44. Digital Input Threshold .............................................................. 2-15
2-45. Digital Input Buffers ................................................................... 2-15
2-46. Digital and Alarm Output Drivers .............................................. 2-15
2-47. Totalizer Input ............................................................................ 2-16
2-48. External Trigger Input Circuits .................................................. 2-16
2-49. A/D Converter PCA ........................................................................ 2-16
2-50. Analog Measurement Processor ................................................. 2-17
2-51. Input Protection .......................................................................... 2-17
2-52. Input Signal Conditioning .......................................................... 2-20
2-58. Passive and Active Filters .......................................................... 2-25
2-59. A/D Converter ............................................................................ 2-26
2-60. Inguard Microcontroller Circuitry .............................................. 2-27
2-61. Channel Selection Circuitry ....................................................... 2-27
2-62. Open Thermocouple Check ........................................................ 2-28
2-63. Input Connector PCA ...................................................................... 2-28
2-64. Display PCA ................................................................................... 2-29
2-65. Main PCA Connector ................................................................. 2-29
2-66. Front Panel Switches .................................................................. 2-29
2-67. Display ........................................................................................ 2-30
2-68. Beeper Drive Circuit ................................................................... 2-30
2-69. Watchdog Timer and Reset Circuit ............................................ 2-30
2-70. Display Controller ...................................................................... 2-31
2-71. Memory PCA (2625A Only) ........................................................... 2-33
2-72. Main PCA Connector ................................................................. 2-33
2-73. Address Decoding ....................................................................... 2-33
2-74. Page Register .............................................................................. 2-34
2-75. Byte Counter ............................................................................... 2-34
2-76. Nonvolatile Memory ................................................................... 2-34
2-77. IEEE-488 Interface (Option -05) .................................................... 2-34
2A Theory of Operation (2635A)............................................................. 2A-1
2A-1. Introduction .......................................................................................... 2A-3
2A-2. Functional Block Description............................................................... 2A-3
2A-3. Main PCA Circuitry......................................................................... 2A-3
2A-4. Power Supply............................................................................... 2A-3
2A-5. Digital Kernel .............................................................................. 2A-3
2A-6. Serial Communication (Guard Crossing).................................... 2A-6
2A-7. Digital Inputs and Outputs........................................................... 2A-6
2A-8. A/D Converter PCA......................................................................... 2A-6
2A-9. Analog Measurement Processor.................................................. 2A-6
2A-10. Input Protection Circuitry............................................................ 2A-6
2A-11. Input Signal Conditioning ........................................................... 2A-6
2A-12. Analog-to-Digital (A/D) Converter............................................. 2A-6
2A-13. Inguard Microcontroller Circuitry............................................... 2A-6
2A-14. Channel Selection Circuitry ........................................................ 2A-7
2A-15. Open Thermocouple Check Circuitry.......................................... 2A-7
2A-16. Input Connector Assembly .............................................................. 2A-7
2A-17. 20 Channel Terminals.................................................................. 2A-7
2A-18. Reference Junction Temperature................................................. 2A-7
2A-19. Display PCA .................................................................................... 2A-7
2A-20. Memory Card Interface PCA........................................................... 2A-7
2A-21. Detailed Circuit Description ................................................................ 2A-7