Fluke RUSKA 7252, User Manual

Page: 32 / 128

RUSKA 7252
Users Manual
2-12
Case Reference Vacuum Sensor - Option
A case reference vacuum sensor is a user selectable option. This option includes a
vacuum sensor installed into the test port on absolute units and the sensor case reference
port on differential units and can be read directly by the Calibrator.
On permanent absolute instruments, this is used to zero the RUSKA quartz sensor. Please
note that the uncertainty of the vacuum sensor used to zero the Calibrator must be
considered in the overall uncertainty analysis of the Calibrator.
On units that have been purchased with the “Absolute Mode with Evacuated Reference”,
this sensor is used to zero the Calibrator and it is used to continuously monitor the
Calibrator Case reference while operating in the absolute mode.
Software
The Calibrator is a digital, software-based instrument. The controlling software uses a
PID algorithm and allows for user-definable units and onboard programming. The
software control loop is a digital outer loop with a high speed inner loop.
Software Safety Controls
Preventing Operator Errors
The operator is required to verify a change to Control mode or Vent mode by pressing the
Enter key. Additionally, the control set-point is set to zero on power-up or when any of
the limit errors occur.
Pneumatic Errors
The Calibrator continually monitors the pressure for low, high and slew (rate of change)
limits. When these limits are exceeded, the Calibrator is returned to Measure mode, shuts
off the apply and exhaust control valves, and an error message is generated. Additionally
a vent limit may be set. The Calibrator will go to Vent mode when the pressure exceeds
this limit.
Shut Offs
Measure mode can be entered at any time by pressing the Measure key on the main
keypad with no further acknowledgment required. The Calibrator will turn off the
controller.
Oven Control
The oven temperature is controlled via a pulse-width modulated signal. The time the
heater is on can be varied from 0% to 100%. The pulse-width at startup is initialized to
the previous value which was stored in battery-backed CMOS RAM.
The oven control is a PID controller updated approximately every 7 seconds. The sensor
readings are accessed by pressing
Menu | Menu | Display | Temp.
With an exception
of the 3000 psi (20.7 MPa) version RUSKA 7252, the high accuracy quartz sensor is
housed in a temperature controlled oven. There is a 3 hour warm-up time required prior
to the Calibrator operating at its optimum precision. The user can verify when the
instrument is thermally stable by viewing the
Menu | Menu | Display | Temp
screen
and verifying that the temperature is at 50
o
C. In addition to the temperature, this screen
will show the duty cycle of the oven.
When operating the system in either a very cold or hot environment, if the oven in unable
to maintain the temperature of the internal oven, the Calibrator will generate an
Oven
Control Failure
error messages. The operator can review the temperature and duty
cycle of the oven by pressing the
MENU | MENU | DISPLAY | TEMP
keys. The unit
must have been warmed up for a minimum of 3 hours prior to determining the condition
of the oven temperature control. The temperature of the sensor should be controlled to