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Ps Absolute Sensor — VAC Level
A high capacity vacuum pump must be connected to the rear vacuum port.
The RUSKA 7750i has a Vacuum Sensor mounted internal to the primary sensor housing
that monitors the vacuum level of the Ps sensor when the sensor is being zeroed. This
sensor reading will display a value of 350 mtorr when the vacuum level is at or greater
than 350 mtorr.
1. Select the desired vacuum units using the UNITS key. You can change both the unit
of measure that the ADTS is displaying Pressure and the unit of measure for the
vacuum sensor. It is not required to have the ADTS displaying pressure in the same
unit of measure as the vacuum sensor. To change the unit of measure for the Vacuum
sensor, press the UNIT key and then the Vacuum [F2] key.
2. Enter the Calibration screen by selecting MENU | MENU | CALIBRATE.
3. Select Zero [F1]. DO NOT press the Calibrate button. When initiating the zeroing
command in the ADTS, it will cycle the internal valves allowing the external vacuum
pump to pull a hard vacuum on the RUSKA sensor. It is recommended that the
sensor be pulled down to a vacuum of less than 100 mtorr (preferably less than 60
mtorr) in order to obtain a proper zero. The ADTS can be zeroed at higher vacuum
levels, however, the uncertainty of vacuum sensors tend to increase at higher vacuum
levels, therefore, the uncertainty in the ADTS would also increase if zeroed at higher
vacuum levels.
4. Wait for the vacuum level to stabilize as read by the internal vacuum sensor.
Generally the stability should to be better than 5 mtorr per minute.
5. Verify that the primary sensor pressure and temperature are stable.
6. Press OK [F6] when stable.
7. Do not disturb the instrument while zeroing is in process.
8. Wait for the zeroing procedure to finish.
9. Press PREVIOUS to return to the Main Menu.
Sensor Photocell Zeroing
If the error message "Mechanical Zeroing Needed" is displayed, the sensor photocell
must be zeroed. The following steps describe this process. Press the MODE key to select
the desired channel.
The ADTS should only be opened by qualified
electrical/mechanical service technicians. Lethal voltages are
present and exposed in the power supply and display.
The Qc sensor MUST have zero differential pressure between the Test Pt
port and Reference Ps port. The Ps sensor requires a vacuum of
<200 mtorr.
1. Remove the ADTS's top cover—the Ps sensor is located on the right, and the Qc is
on the left (when viewed from the front of the unit).
2. Locate and remove the plastic zeroing plug located in the side of the sensor oven
assembly.
3. Enter the Zeroing screen by selecting MENU | MENU | CALIBRATE.
WX Warning
Note
Maintenance
Sensor Photocell Zeroing
6
6-9
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