ENMET ISA-44-RALE-OD - Manual (Page 23)

ISA-44RALE-OD/ISA-44RAHE-OD/ISA-44E-OD ENMET Corporation
19
6.0 Calibration 6.0 Calibration
Calibration is essentially an adjustment of the circuitry affecting the instrument response to particular concentrations of
gas or oxygen. Utilizing controlled concentrations of these gases, the user exposes the sensors to these gases and then
adjusts the appropriate potentiometers to set alarm points, full scale readings or other responses.
Potentiometers are the most essential components in calibration located directly on the circuit boards of the ISA-
44RALE-OD, potentiometers change resistances in circuits, altering certain voltages. This affects the response of the
instrument. Potentiometers are adjusted by turning a small screw in the potentiometer. Since there is always a short lag
time between an adjustment and its affect on the circuit, always wait a few seconds after making an adjustment to see how
much the voltage has been affected.
When using controlled concentrations of gas to calibrate the instrument, do not expose the sensors to this gas if it is
flowing directly from compressed air cylinders. Such gas is extremely dry and will not provide accurate calibration. The
gas must be humidified by flowing through the bubbler on the ISA-44RALE-OD sample head assembly. Also, do not
gas set in a background of pure inert gas, such as argon or nitrogen. The MOS sensor will pick up the background gas
and render an inaccurate reading. Appropriate calibration gases are available from ENMET.
The oxygen portion of this unit is the same as for the ISA-44RALE-OD. The gas portion of this unit will change
depending on the end users criteria. As in the ISA-44RALE-OD the alarm points are preset at the factory and calibration
information can be found labeled on the display plate of the unit.
C AUTION : If the covers of either the control unit or the MOS sensor enclosure are removed, the enclosures are no longer
explosion proof.