
5725A
Instruction Manual
4-26
Integrator
4-42.
Op amp U601A is configured as an integrator to reduce the output offset of the input
amplifier circuit. This integrator senses the output voltage of the amplifier (MVOUT)
through R604 and R605 and forces it to be zero with respect to HVCOMM.
Window Comparator
4-43.
Comparators U604A and U604B form a window comparator that monitors the output of
the input amplifier, U602. The window is set to about +2.2V to +9V by R626, VR602,
and R636. If the output of U602 exceeds the window limits, the appropriate comparator
turns on the clamp, Q604, shorting the input to ground. The comparator also pulls
control line CLAMPS high via U604D, where the comparator routes to the Digital
Assembly (A5) through the Interconnect assembly (A1). Comparator U604D is a level
shifter to translate the window comparator output to a TTL level.
Exceeding the limits of the window comparator is an indication that the loop is in an
abnormal condition when the instrument is in the ac voltage standby or ac voltage
operate states. In current standby or current operate states, the comparator causes
CLAMPS to be asserted, which turns off the +400V and -400V supplies.
Input Clamp
4-44.
A FET clamp, Q604, is turned on until the output of U602 returns to the region within
the window. When this occurs, the comparator turns off Q603. To avoid a large transient
at the output of the High Voltage Amplifier assembly (A6), the clamp must be turned off
slowly. Resistor R637 and C618 slow the clamp drive signal to accomplish this. Though
Q604 can be turned off slowly by removing its gate drive slowly, it clamps
asymmetrically in the transition region. The body of the FET is held at -7.5V. This keeps
the FET from turning on at the negative peaks of the input waveform. The asymmetrical
clamping appears as a dc shift in the waveform, which can cause the transformer to
saturate. To alleviate this problem, a second clamp is placed in parallel with Q604.
This second clamp is the photoresistor portion of the optical isolator, U605. It has a
considerably higher on resistance than Q604, so the two are used together. When the
clamp is to be turned off, Q603 is turned off and the voltage on C618 begins its
transition from 15V to -15V. At +15V, Q604 is turned on but because Q605 is
also on, shunting current from the input of U605, the photoresistor is in the high
impedance state. When the voltage on C618 reaches about +9V, Q605 turns off and the
optoisolator is turned on, putting the photoresistor into its low resistance state. This has
little effect on the input signal because the photoresistor is a higher impedance than the
FET. As the control voltage approaches zero, Q604 turns off and the input is clamped
only by the photoresistor. As the control voltage continues toward -15V, the
photoresistor makes the transition to its off, or high impedance state. The photoresistor
clamps symmetrically, eliminating the dc transient on the input. A similar transition
takes place when light turns on the clamp but it happens much faster, as the turn-on
transition is controlled by the time constant R631*C618 which is about an order of
magnitude faster than the R637*C618 turn-off time constant.
The microprocessor on the Digital assembly can also pull the clamp via control line
CLAMPD, which is latched into a driver on the High Voltage Sense assembly (A6). Line
CLAMPD is asserted during a sequenced turn on, power down of the High Voltage
Amplifier assembly (A3), or during a transition to another frequency range. Comparator
U604C level shifts CLAMPD and provides an OR function with the window comparator
output.
Summary of Contents for 5725A
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Page 62: ...5725A Instruction Manual 4 4 Figure 4 1 5725A Overall Block Diagram...
Page 78: ...5725A Instruction Manual 4 20 aq20f eps Figure 4 3 Current Amplifier Assembly Block Diagram...
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Page 132: ...5725A Instruction Manual 8 6 aq24f tif Figure 8 1 Final Assembly...
Page 133: ...List of Replaceable Parts 8 8 7 aq25f tif Figure 8 1 Final Assembly cont...
Page 134: ...5725A Instruction Manual 8 8 aq26f tif Figure 8 1 Final Assembly cont...
Page 135: ...List of Replaceable Parts 8 8 9 aq27f tif Figure 8 1 Final Assembly cont...
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Page 137: ...List of Replaceable Parts 8 8 11 aq29f tif Figure 8 1 Final Assembly cont...
Page 138: ...5725A Instruction Manual 8 12 aq30f tif Figure 8 1 Final Assembly cont...
Page 139: ...List of Replaceable Parts 8 8 13 aq31f tif Figure 8 1 Final Assembly cont...
Page 141: ...List of Replaceable Parts 8 8 15 5725A 1611 aq36f eps Figure 8 2 A1 Interconnect PCA...
Page 145: ...List of Replaceable Parts 8 8 19 5725A 1650 aq37f eps Figure 8 3 A2 Current Amplifier PCA...
Page 149: ...List of Replaceable Parts 8 8 23 5725A 1661 aq38f eps Figure 8 4 A3 High Voltage Amplifier PCA...
Page 153: ...List of Replaceable Parts 8 8 27 5725A 1631 aq39f eps Figure 8 5 A4 Power Supply PCA...
Page 155: ...List of Replaceable Parts 8 8 29 5725A 1650 aq40f eps Figure 8 6 A5 Digital PCA...
Page 159: ...List of Replaceable Parts 8 8 33 5725A 1601 aq41f eps Figure 8 7 A6 High Voltage Sense PCA...
Page 161: ...List of Replaceable Parts 8 8 35 aq32f tif Figure 8 8 A12 Transformer Enclosure Assembly...
Page 162: ...5725A Instruction Manual 8 36 aq33f tif Figure 8 8 A12 Transformer Enclosure Assembly cont...
Page 163: ...List of Replaceable Parts 8 8 37 aq34f tif Figure 8 8 A12 Transformer Enclosure Assembly cont...
Page 164: ...5725A Instruction Manual 8 38 aq35f tif Figure 8 8 A12 Transformer Enclosure Assembly cont...
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Page 169: ...Schematic Diagrams 9 3 9 Figure 9 1 A1 Interconnect PCA 5725A 1611 aq48f eps...
Page 170: ...5725A Instruction Manual 9 4 Figure 9 1 A1 Interconnect PCA cont...
Page 171: ...Schematic Diagrams 9 5 9 Figure 9 1 A1 Interconnect PCA cont...
Page 172: ...5725A Instruction Manual 9 6 Figure 9 2 A2 Current Amplifier PCA 5725A 1650 aq52f eps...
Page 173: ...Schematic Diagrams 9 7 9 Figure 9 2 A2 Current Amplifier PCA cont...
Page 174: ...5725A Instruction Manual 9 8 Figure 9 2 A2 Current Amplifier PCA cont...
Page 175: ...Schematic Diagrams 9 9 9 Figure 9 2 A2 Current Amplifier PCA cont...
Page 176: ...5725A Instruction Manual 9 10 Figure 9 3 A3 High Voltage Amplifier PCA 5725A 1661 aq56f eps...
Page 177: ...Schematic Diagrams 9 11 9 Figure 9 3 A3 High Voltage Amplifier PCA cont...
Page 178: ...5725A Instruction Manual 9 12 Figure 9 3 A3 High Voltage Amplifier PCA cont...
Page 179: ...Schematic Diagrams 9 13 9 Figure 9 4 A4 Power Supply PCA 5725A 1631 aq59f eps...
Page 180: ...5725A Instruction Manual 9 14 Figure 9 4 A4 Power Supply PCA cont...
Page 181: ...Schematic Diagrams 9 15 9 Figure 9 4 A4 Power Supply PCA cont...
Page 183: ...Schematic Diagrams 9 17 9 Figure 9 5 A5 Digital PCA cont...
Page 185: ...Schematic Diagrams 9 19 9 Figure 9 6 A6 High Voltage Sense PCA cont...
Page 186: ...5725A Instruction Manual 9 20 Figure 9 6 A6 High Voltage Sense PCA cont...
Page 187: ...Schematic Diagrams 9 21 9 Figure 9 6 A6 High Voltage Sense PCA cont...
Page 188: ...5725A Instruction Manual 9 22 Figure 9 6 A6 High Voltage Sense PCA cont...
Page 189: ...Schematic Diagrams 9 9 23 aq45f eps Figure 9 7 A12 Transformer Enclosure Assembly...
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