Fluke RUSKA 7252, User Manual

Page: 25 / 128

Theory of Operation
Pneumatics Module
2
2-5
PRIMARY SENSOR
INNER LOOP CONTROL SENSOR
SUPPLY
PRESSURE PORT
EXHAUST
PORT
RELEASE APPLY
ISOLATION
ZERO
TEST
PORT
REFERENCE
PORT
V
VACUUM
SENSOR
Option
Control Section
glb04.eps
Figure 2-3. RUSKA 7252 Calibrator Absolute Pneumatics Diagram to 50 PSIA (340 kPa) FS
Note
This diagram depicts only one of the two RUSKA 7252 channels.
Table 2-2. Solenoid Valves States
Valve Measure Mode Vent Control Mode Zeroing
Test Port Isolation open open open close
Zero close close-open close open
Apply close close modulate close
Release close open-close modulate close
Measure Mode Pneumatics
Figures 2-2 and 2-3 summarize the Pneumatics of the Calibrator.
Reference Port
For gauge measurements, the Reference Port is normally left open to atmosphere.
The Reference Port is isolated from the Test Port by a solenoid valve that is closed during
the Calibrator’s Measure and Control modes. When the user commands the Calibrator to
perform the zeroing process, the solenoid automatically opens, and the pressures on the
Reference Port and Test Port become equal. On permanent absolute instruments, it is
recommended to tie the reference port to the exhaust port and then connect them to the
vacuum pump. Therefore, when the unit is zeroed, the reference port valve opens, and a
vacuum is pulled onto the test port allowing the instrument to zero at a low vacuum level.
The Reference Port is protected by a relief valve.