Prevac MG15 - Page 61

MULTI GAUGE CONTROLLER OPERATION
Excessive emission current
High emission current for relatively high values of pressure may damage the
sensor. The emission current may be set at a given value only when the user is
sure that the gauge will be operated at appropriately low pressures.
2. SENSITIVITY FACTOR
The function describing the dependence between the gas type, gauge geometry and temper-
ature is generally deined as gauge sensitivity factor 𝑆

.
The factor can be expressed in the following formula:
𝑆

=




⋅
where:
𝑆

- sensitivity factor for a given gas g
𝐼

- ion current, see ig. 3.40
𝐼

- emission current, see ig. 3.40
𝑃
- pressure
Sensitivity factor 𝑆

is strictly connected with a gauge type. Its value may be set between 0.05
and 100. Sensitivity factor is also called calibration factor in speciications of extractor gauge
manufacturers.
Note
For precise measurements always set an appropriate sensitivity/calibration
factor. This parameter is speciied by the gauge manufacturer - it can be the
same for all gauges of a given type, and in some cases it is strictly connected
with the serial number of the gauge.
3. DEGAS POWER
The MG15 is used during degassing the electron bombardment method. The power with
which the gauge is degassed may be set between 1 and 40 W. This value should be set accord-
ing to the manufacturer’s speciications. The ramp rate of power after activating degassing
is set at 1 W/s and cannot be changed. To activate degassing and set its duration enter the
Degas menu, see chapter 3.6.2. It is recommended, if possible, to degas with power lower
than the nominal one by extending adequately degassing time. It is done to extend the life of
the ilament.
4. CALIBRATION PARAMETER SETTING
Note
The calibration parameter is deined by some manufacturers of vacuum gauges.
The value of this parameter is individual for each gauge and provided by the
manufacturer together with the gauge.
This parameter should be set according to the calibration factor of a given gauge. If this factor
is missing or lost, contact directly the gauge manufacturer and state its serial number.
User manual rev. 03 Page 61