Installation, Operation and Service Manual
LKP Series
© 2016 DynAmp, LLC
Page 28
041749 K
6.9 COMPARATORS AND PULSE GENERATOR
The comparators consist of U110 and U111. They compare the amplified and filtered
output of the error amplifiers to the two ramps generated by PLL and ramp generators.
Two square waves are generated at the output of these comparators, one for the positive
half cycle and one for the negative half, (pins 1 and 2 of U110 for channel #1). One square
wave will be used to trigger an SCR on the positive half of the waveform, and the other will
be used for the other half cycle. Since these square waves are too long in duration, they
cannot be used directly to drive the pulse transformer drivers. The comparator output is
"ANDed" (the mathematical product of a logic AND gate) with several pulses generated by
the PLL. The output, (pins 3 and 4 on U113 for channel #1) will be a pulse train which will
be used to drive the pulse transformer drivers. Pulse train triggering is an advantage when
noise on the line turns off an SCR. The SCR is retriggered allowing a minimum off time.
Since these pulses are fixed and do not move, if they alone were used to drive the SCRs,
the output would be very jumpy. This was smoothed by also anding the comparator with
an integrated output of itself to give the output pulse train infinite resolution.
6.10 PULSE TRANSFORMER DRIVERS
The pulse transformer drivers consist of U203, U204, and associated circuitry. A pulse
train signal is sent into the drivers (pin 2 and 1 of U203 for channel #1). These drivers are
open collector outputs, which drive the pulse transformers (T203A and T203B for channel
1). The secondary of the pulse transformer develops a current pulse which drives the
associated SCRs (SCR pack #1 for channel #1).
6.11. OUTPUT CIRCUIT
Six outputs are provided by the system:
1. A standard voltage output of 1 mV/kA, at TS2-7 and TS2-8.
2. An optional secondary voltage output, at TS2-9 and TS2-10.
3. A current output of 1 Adc per 5 kA of bus current, at TS2-5 and TS2-6. The current
output is available by removing a jumper connected across the TS2 terminals (do not
remove the jumper while the system is energized). Maximum allowable voltage drop
across the terminals is 15 Vdc at maximum bus current.
4. A normally open (N.O.) contact for the Metering Unit over temperature alarm, rated at
120 Vac, 6 A, at TS2-11 and TS2-12.
5. A normally closed relay contact for accuracy diagnostics output at TS2-17 through TS2-
19. This feature is only available when the accuracy diagnostics option is ordered.
6. Optional isolated shunt output. Scaling is per customer order: 0-10V, 4-20mA
available.
Burden resistors inserted in the series output circuit should be selected with care. The
wattage rating should be at least two times higher than the calculated power dissipation.
The burden resistor should have a low temperature coefficient (25 ppm or better).
The Metering Unit is supplied with a two-pole circuit breaker mounted inside the enclosure,
on the main panel.
