Electrical Test Instruments PI-6000
Section II - Detailed Description
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Page II-8
control panel to provide 12 VDC. Transformer T6, protected by fuse F5, steps it
down by a factor of ¼, and this voltage is sensed by a voltage relay circuit. When
the primary voltage is between about 200 and 270 VAC, this circuit allows
operation in 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.
When the input voltage selector switch S11 is the 208/240 V position, relay K9 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
input 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
voltage 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, relay K2 on the voltage sensor 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 K10 is energized, which provides 120 VAC control
power to the entire test set, including the fans and the auxiliary GFI outlet,
protected by 8 ampere circuit breaker CB1.
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
current power to the test set output circuitry through the SCR controller. The
switched output voltage is supplied to distribution blocks DB1 and DB2.
The rheostat autotransformer T1 and output transformer T2 are connected to
input voltage selector switch S11. This allows for connection in series for 480 VAC,
and parallel for 208/240 VAC. Rheostat T1 is connected directly to the first
primary of T2, so that clockwise rotation produces an output voltage of about 0-
1.5 VAC. Relays K1, K2, and K3 connect the second primary windings for fixed
outputs of 0, 1.25, or 2.50 VAC for taps 1, 2 and 3. For subsequent taps, the large
sections T2C, T2D, and T2E are added to the circuit, while the second section
alternates between 1.25 and 2.5 VAC, for a series of nine (9) overlapping output
ranges up to 11.5 VAC.
