SAFETY & INSTALLATION INSTRUCTIONS FOR
HP & KS SERIES FITTED WITH CURRENT MONITOR 		September
2001
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 1.0µF 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 100µA on the HP series (except HP10P, HP10N, HP10R = 50µA, HP20P, HP20N & HP20R = 33µA & HP30P, HP30N & HP30R= 50µA) and 50µA on the KS series.

Unit type and output voltage Load current Measured current on simple current monitor
HP series at full voltage * 0µA    100µA
HP series at half voltage * 0µA    50µA
HP series at full voltage * 10µA    110µA
HP series at half voltage * 10µA    60µA
KS series at full voltage 0µA    50µA
KS series at half voltage 0µA    25µA
KS series at full voltage 10µA    60µA
KS series at half voltage 10µA    35µA
   * 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.
Simple i-mon SIMPLE CURRENT MONITOR
METER READS ACTUAL CURRENT PLUS INTERNAL FEEDBACK CURRENT (HP SERIES 100µA, KS SERIES 50µA AT FULL OUTPUT)
Precision i-mon +ve CURRENT MONITOR WITH INTERNAL FEEDBACK CURRENT REMOVED

POSITIVE POLARITY UNITS

Precision i-mon -ve CURRENT MONITOR WITH INTERNAL FEEDBACK CURRENT REMOVED

NEGATIVE POLARITY UNITS

NOTES:
1 : R6 & R16 total 100k ohm including 10k source resistance.   For accurate measurements of less than 1µA replace with potentiometer and trim for accurate ZERO.
2 : Make R3 & R13 10k ohm to read 10V = 1 mA and 100k.ohm to read 10V = 100 µA.
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