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Precision Current Monitor
Units fitted with the optional precision current monitor have
the circuit shown below fitted internally and give 0 to 10V to represent
0 to maximum current. The information below does not apply to units
fitted with precision current monitor and if unused a resistor is
not required from pin 8 to pin 9.
Simple Current Monitor
For units fitted with a simple stack return type current monitor,
current is measured between pin 8 (HPR reversible units use pin
1 instead) and pin 9 (0 volt). The polarity of the voltage on pin
8 is opposite to the unit polarity. IF UNUSED PIN 8 SHOULD BE JOINED
TO PIN 9, IF THIS IS NOT DONE THE INTERNAL NEON BULB WILL FLASH
PERIODICALLY.
Protection during arcing is by an internal 1.0 uF capacitor and
neon bulb. If a resistor is fitted between pins 8 (HPR units pin
1) & 9 then a voltage of up to 50 volts will be produced. A
high voltage may degrade the load regulation of the unit.
The current measured includes internal feedback currents used
to control the unit. These currents are proportional to the output
voltage and are 100 uA on the HP series (except HP10P, HP10N, HP10R
= 50 uA, HP20P, HP20N & HP20R = 33 uA & HP30P, HP30N &
HP30R= 50 uA) and 50 uA on the KS series.
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Unit type and output voltage
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Load current
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Measured current on simple current monitor
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HP series at full voltage *
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0 uA
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100 uA
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HP series at half voltage *
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0 uA
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50 uA
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HP series at full voltage *
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10 uA
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110 uA
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HP series at half voltage *
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10 uA
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60 uA
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KS series at full voltage
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0 uA
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50 uA
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KS series at half voltage
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0 uA
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25 uA
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KS series at full voltage
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10 uA
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60 uA
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KS series at half voltage
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10 uA
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35 uA
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* Except HP10P, HP10N, HP10R, HP20P, HP20N, HP20R, HP30P &
HP30N, HP30R.
The I monitor signal can be used in 3 ways:
1/ Remove the feedback current by calculation.
2/ Feeding the signal to a computer which can compute the actual
current from the output voltage.
3/ Feedback back-off circuit see diagram below.
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