Oven Control; Pressure Reading And Correction - Fluke RUSKA 7750i User Manual

RUSKA 7750i
Users Manual

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 that 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. The high
accuracy quartz sensor is housed in a temperature-controlled oven. There is a 3-hour
warm-up time required prior to the ADTS operating at its optimum precision. The user
can verify when the instrument is thermally stable by viewing the MENU | DISPLAY
screen and verifying that the temperature is at 50 ºC. 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 ADTS 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 50 ºC.
The Duty Cycle indicates the amount of time (in units of percentage) that the oven
control is turned on in order to maintain the oven at the proper set point of 50 ºC. A unit
that is operating properly, after it has fully warmed up, should indicate a sensor
temperature of 50 ºC and a duty cycle between 10% to 90%.

Pressure Reading and Correction

The sensor's analog output is processed by an analog-to-digital circuit. This output is
corrected for the applied effects listed below.
The output is linearized and the resulting pressure value is corrected for the variations in
head pressure, vacuum, case effect, and oven temperature effects.
The following equations are used to adjust and correct the pressure signal.
2-10
Figure 2-5. Menu | Display - Menu
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