Theory of Operation
ECO 422
4–5
the select lines is accomplished by cross wiring P_LED and B_LED, through the
buffer to (B_O) and (P_O), which are complimentary.
The high current (ALARM) output is provided by Q32 and a high wattage 22
W
resistor. A 10 k
W
pull-down is provided for test purposes.
The fault reporting output, U15 and Q33, provide a method of fault indication
that also includes remote indication of instrument failure. A 24 V, 20 mA current
limited input and ground are connected to J17–2 and J17–4. When the controller
detects an input fault or suffers a power failure, the LED in U15 shuts off. The
transistor opens up allowing Q33 to saturate to less than 1.5 V, signaling the
fault. When the LED is on, Q33 is cut off leaving less than 100 nA of leakage.
The diodes, CR48 and VR1, are provided for reverse voltage and ESD protec-
tion.
Controller.
The Controller has five main functions:
H
Encode the keyboard signals.
H
Send the correct signals to the LED Driver.
H
Generate the ALARM signal for the Remote circuit.
H
Generate the Switch or Auto Switch command.
H
Keep track of the Time Out circuit.
The five inputs from the Keyboard Encoder enter the Controller. KEY_VALID is
internally delayed three clock cycles to allow key data setup. The ENABLE and
the delayed KEY_VALID signal clock a toggle flip–flop high to enable the three
input gates. Once enabled, the combination of delayed KEY_VALID and each
input produces a control signal for the Controller LED Driver circuit, the
Lockout circuit, and the Fault circuit.
The fault block of the Controller uses four input signals (PFAULT), (BFAULT),
(TIMER), and RESET. These signals determine whether the (ALARM) signal
needs to be sent to the Remote, if the Primary or Backup front panel Alarm
LEDs should be on, and if the auto switch function should be activated. The
RESET command turns off the LEDs and the Remote Alarm output. The
(TIMER) signal is NANDed with the LED fault signal to make it flash.
The automatic source change with fault detection function is enabled by the
(AUTO_O) signal from the Keyboard Encoder circuitry. This signal and some
other controls generate (AUTO_ON). (AUTO_ON) can be switched off by the
(R_AUTO) control from the rear-panel Remote connector. The (AUTO_ON)
signal is also used to derive the (P_SELECT) and (B_SELECT) signals.
(AUTO_ON) and (AUTO_OFF) are sent to drive the front-panel LED circuit.
After the front panel is enabled, the ECO 422 will only allow the front panel
approximately 60 seconds of inactivity before it will automatically disable the
Summary of Contents for ECO 422
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Page 14: ...General Safety Summary viii ECO 422 ...
Page 16: ...Service Safety Summary x ECO 422 ...
Page 17: ...Getting Started ...
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Page 31: ...Operating Basics ...
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Page 41: ...Operating Basics ECO 422 2 9 Figure 2 6 Setup for Adjusting R265 the User Level for SX 7 ...
Page 43: ...Specifications ...
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Page 53: ...Theory of Operation ...
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Page 62: ...Theory of Operation 4 8 ECO 422 ...
Page 63: ...Performance Verification ...
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Page 84: ...Performance Verification 5 20 ECO 422 ...
Page 85: ...Adjustment Procedure ...
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Page 88: ...Adjustment Procedure 6 2 ECO 422 ...
Page 89: ...Maintenance ...
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Page 101: ...Options ...
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Page 104: ...Options 8 2 ECO 422 ...
Page 105: ...Replaceable Electrical Parts ...
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Page 141: ...Diagrams Circuit Board Illustrations ...
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Page 147: ... ECO 422 Changeover Unit FRONT PANEL 1 ...
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Page 167: ...Replaceable Mechanical Parts ...
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Page 176: ...ECO 422 A1 FIG 1 EXPLODED VIEW A2 A3 A4 ...
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