Electrical Test Instruments PI-2500-G2 & PI-5000-G2
Section II - Detailed Description
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Page II-2
Primary protection is provided by high capacity 400 ampere input fuses (F1 and
F2). After that, the control section is protected by smaller 5 ampere fuses (F3 and
F4), and the power section is isolated by means of high current contactors (K13
and K14).
Transformer T6, protected by fuse F6, steps down the primary voltage by a factor
of ½, and is connected to a wide range switching power supply in the indicator
control panel to provide 12 VDC. The dual primary of transformer T6 steps it
down by a factor of 1/2, and T10 steps it down by another factor of ½, and this
voltage is sensed by a voltage relay circuit and read on the control panel LED
meter. When the primary voltage is between about 200 and 270 VAC, this circuit
allows operation in 208 or 240 VAC mode. If the voltage is between about 420
and 520 VAC, operation is allowed in 480 VAC mode. Control power cannot be
turned on if the voltage is outside these bounds.
Another transformer, T9, supplies nominal 104, 120 or 240 VAC power to the con-
trol panel, which has an internal 12 VDC power supply which powers other por-
tions of the control circuitry of the control PCB.
When the input voltage selector switch S1 is the 208 or 240 V position, relay K6
is energized, setting the primary windings of transformer T4 in parallel. This also
energizes relay K1 on the voltage sensor PCB and provides an interlock and in-
put selector error indication. The voltage sensor PCB rapidly flashes the Input
Select Error LED on the control panel for 5 seconds during startup, and then
turns off if input voltage is within bounds as determined by the input selector
switch position. If line voltage is incorrect, the Input Select Error LED will flash,
and control power cannot be turned on. If control power is energized, brief volt-
age sags or surges will flash the LED as a warning. If such voltage excursions
persist for longer than about 0.2 seconds, the control power will drop out.
Binding post BP1 is provided for separate connection to an earth ground, to
check for ground integrity. When there is continuity from this point to chassis
ground, a relay on the control PCB is energized, and enables the interlock for
control power. If ground integrity is not sensed, the Ground Open LED DS1 will
light. A separate lead should be connected to the external equipment ground
system to verify that the main grounding cable is intact. Do not defeat this
safety feature by jumpering the ground binding post to the test set frame.
When the control power switch in the indicator control panel is pressed, and all
voltage interlocks are OK, relay K7 is energized, which provides 120 VAC control
power to the auxiliary GFI outlet, protected by 4 ampere circuit breaker CB1. A
relay on the control PCB provides 120 VAC control power to the entire test set,
including the fans and the main contactors. In 208 V input mode.
If all power interlocks are OK, the Main Power switch in the indicator control
panel may be pressed to activate main contactors K13-14. This provides high cur-
rent power to the test set output circuitry through the SCR controller. The
