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The
packaging configuration for the
ATE-30 and ATE-31 Potential Transformer Interface (PTInterface) modules
is
shown in the two pictures above. The circuit board layout and
design are
essentially the same; the electronic circuitry and electrical
performance of
these two modules are identical. The original ATE-31
was designed
into the Weidmuller DIN rail mount (23 mm wide)
packaging. This
enclosure did not meet the CIE flame retardancy standards, so the
design was
improved by switching to the Phoenix Contact (23 mm
wide) DIN rail
mount enclosure.
Both
of these signal
conditioners utilize the Analog Device AD210 isolation amplifier as the
primary
element, providing up to 3500 VDC isolation between the input
and the
output.
For
this design and CIE
certification, the isolation was tested to 2000 VDC
isolation. Both
designs have the same electronic circuit in them.
The
input accepts a voltage from an
instrumentation potential transformer and converts it to a 24 Volt
pulse train
for use by PLC-based frequency counting equipment. The input
amplitude
can vary from 0.2 VRMS to 180 VRMS. The input frequency can
vary from 6
Hz to 120 Hz.
A 180
Hz 3-pole Butterworth
low-pass filter in the ATE-3X PTInterface prevents high frequency
noise, such
as that induced by operation of nearby switchgear from getting
to the
tachometer input. This filter blocks high frequency
transients
that may be superimposed upon the input signal
voltage from passing
through to the frequency counting equipment.
The
amplifier sensitivity of the
Model ATE-31 allows it, in conjunction with a frequency
counter, to
reliably measure the frequency output of a generator operating at low
speed
prior to the application of field excitation.
Typical
generator output at 10%
speed is greater than 0.2VAC.
The
ATE-31 takes advantage of the
residual magnetism in the rotor and armature of the generator when the
unit is
"off-line."
When
generator excitation is turned
off and the unit is governed in an isolated, "speed-control"
mode.
Accurate
and instantaneous information
about turbine rotor angular speed is essential for robust dynamic
control
system performance.
This
residual alternating
voltage is in exact synchronization with speed, and is ideal for a
tachometer
or speed controller.
The
AD-210 amplifier circuit produces a 24 v
pulse train from a sinusoidal input; intended
to measure the
generator's residual voltage output while spinning at less than 100%
speed,
with generator excitation off.
When
the excitation is on, the 110
VAC output of the PT circuit is sensed using a 15k Ohm 5W resistor and
a pair
of high-speed switching diodes.
The
input
stage of the Model ATE-31 is fully isolated from the output stage, so
the
signal input can be connected either from line to neutral or from line
to line
of the instrumentation potential transformers. The connector plugs are available in two styles, a screw-terminal and a spring-cage type. Two
schools of thoght exist on which is the superior method, the simple
solution for ATECo is to offer both, and let each customer decide which
to use. The PT Interface
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