MKS HPS 947 Series, Руководство по эксплуатации и обслуживанию, Страница: 38 / 40

HPS
®
Products Series 947 CEP System A.2
The Series 947 CEP System Design Overview
This section is intended to give the reader an overview of the internal
workings of the Series 947 CEP System. This manual does not provide
sufficient detail for advanced levels of troubleshooting. Refer to the block
diagram while reading this section.
Bridge Amplifier
The Sensor uses a wire as one arm of a balanced Wheatstone bridge. The
bridge amplifier maintains the wire at a constant temperature. Thus, the
bridge driving voltage from the
amplifier is related to the
pressure in the Sensor.
This voltage is buffered by an
op amp and then fed to the
analog output, the Controller's
digital display, and the
comparator circuit.
Output
The analog output is driven by
an op amp. Although it has a
fairly low output impedance, it
is best to measure the analog
output signal with an
instrument having at least 1
M
Ω
of input impedance.
Set Point Relays
A reference voltage and op
amp form a precision
adjustable reference that is
fed to the comparator circuit.
A potentiometer can be
adjusted to the proper voltage
to trigger the set point relay at
the desired pressure.
Comparator
An analog comparator circuit compares the voltage from the buffer amplifier
(pressure signal) to the set point. When the pressure signal falls below the
adjusted reference voltage, a transistor turns on, which energizes the set
point relay. A resistor provides a feedback path around the op amp, which
increases the set point voltage by approximately 10 mV. This hysteresis
provides stable operation even though some noise may be present on the
buffered output signal.
Atm adjust
Zero Adjust
Buffered Analog Output
Bridge
Amp
X
A/D
Converter
micro-
controller
Comparators
Relay
Relay
V
ref
Display 8. 8. 8. 1.
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