Features:
- Creates isolated optical feedback from two high-voltage bridge measurements.
- Uses independent voltage-to-frequency channels for field current and field voltage.
- Adapts bridge voltage through seven selectable scaling networks.
The current circuit starts with the small millivolt signal produced by the dc shunt at the power-converter output.
A parallel voltage circuit senses the bridge output after resistor selection has reduced the high potential to the amplifier range.
Both converter outputs drive optical transmitters, keeping the controller-side EISB electrically separated from the power bridge.
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Following field-current conversion
- Sensing point: The current shunt sits in the dc output path from the power converters.
- Input level: Its nominal 100 mV signal feeds a differential amplifier.
- Analog span: The amplifier drives a bipolar range from -5 V to +5 V.
- Pulse output: A proportional optical frequency represents the measured field current.
Selecting the bridge-voltage range
- Resistor banks: Jumper-selected networks attenuate bridge output before amplification.
- Seven choices: Each selector position corresponds to a supported application range.
- Common mode: The measurement circuit is designed around high bridge potential relative to control ground.
- Matching rule: A replacement must copy the original selector position unless the bridge design changes.
Maintaining isolated controller feedback
- Dual fibers: Separate optical channels carry current and voltage information.
- EISB receiver: Both signals terminate at the controller communication interface board.
- Noise immunity: Optical transmission avoids conductive pickup across cabinet sections.
- Frequency span: Each converter produces a linear 0-2 MHz signal over its measuring range.
Commissioning the feedback circuits
- Supply conversion: External bipolar dc power is converted into the internal logic and analog rails.
- Polarity check: The shunt leads must preserve sign before field current is applied.
- Range confirmation: Verify the voltage-selector setting against the installed SCR bridge.
- Channel proof: Test current and voltage feedback separately because one path can operate while the other fails.