Inficon SQM-160, Operating Manual

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SQM-160 Operating Manual
3.6 Sensor Frequency
Sensor Min/Max frequencies establish the operating range for the sensing quartz
crystals. Both values are used to determine the % life that is displayed in Xtal Life
mode.
When the sensor frequency drops below the minimum (or reads above the
maximum), the SQM-160 indicates a sensor failure by blinking the Crystal Status
display.
To set sensor minimum and maximum frequencies:
1
Press Program to enter Program mode.
2
Press Prev to enter the System Menu.
3
Press Next until FMIN/FMAX is shown.
4
Press the Control Knob to display FREQ MIN.
5
Adjust the Control Knob to the desired minimum operating frequency on
Display 2.
6
Press the Control Knob to accept the minimum value and display FREQ MAX.
7
Adjust the Control Knob to the desired maximum operating frequency on
Display 2.
8
Press the Control Knob to accept the maximum value.
9
Press Program to exit the System Menu and return to normal mode.
Crystals sometimes fail unexpectedly, or exhibit erratic frequency shifts (mode
hopping) before total failure. Depending on the material, crystals may fail well
before the typical 5 MHz minimum. If you find that crystals fail early consistently,
set FREQ MIN to a value higher than 5 MHz to provide a Crystal Life warning
consistent with actual failure.
A sensor crystal with an initial value that exceeds the maximum will also cause a
blinking Crystal status. The maximum frequency can be set slightly above the
nominal values with no effect on accuracy.