DH Instruments PPCK PLUS, Operation And Maintenance Manual

Page: 136 / 150

PPCK+™ Operation and Maintenance Manual
©2001 DH Instruments, Inc .
Page 128
5.6.4 POWER SUPPLIES
•
+12 V DC (± 2 %) @ 3.3 Amps: For internal and external valve actuation, thermal
pressure control unit (TPCU).
•
+5 V DC (± 1 %) @ 3.0 Amps; + 15 V DC (± 3 %) @ 2.0 Amps; -15 V DC (± 3 %) @
0.35 Amps: For the supply of the micro board and driver board electronics.
5.6.5 ON-BOARD BAROMETER
The barometer board supports a barometric range, micromachined silicon sensor, an
ambient temperature sensor and associated electronics. The barometer readings are used
for dynamic atmospheric pressure compensation when measuring gauge pressure with an
absolute reference transducer (see Section 3.4.1). The temperature sensor is used for
temperature compensation of the barometric sensor. The barometer board includes a
memory in which its specific calibration coefficients are stored.
5.6.6 MICRO CARD
The micro card supports a Motorola 68302 microcontroller; EPROM, EEPROM, NVRAM and
flash memories; RS232 communications; IEEE-488 communications; the front panel keypad
and display control; and a two channel frequency counter for reading the reference
pressure transducers. An I/O port controls other boards and devices in PPCK+.
5.6.7 THERMAL PRESSURE CONTROL UNIT (TPCU)
The PPCK+ thermal pressure control unit is used for fine pressure control in dynamic control
mode (see Section 3.1.2.3). It is a high pressure volume containing a helicoidal
heating element. The TEST and DRAIN ports are machined in to the volume.
5.6.8 REFERENCE PRESSURE TRANSDUCER (RPT)
A PPCK+ has a single reference pressure transducer (RPT) used to measure the high
pressure gas the PPCK+ controls. The RPT’s basic sensing principle is the measurement of
the change in the natural oscillating frequency of a quartz tuning for with temperature and
mechanical stress resulting from the change in pressure applied to a connecting
bourdon tube. Two independent quartz elements are used: one is subjected to pressure
related stress; the other is used only to monitor temperature. Every RPT has three ranges.