ENMET ENG – 97D STAND-ALONE - Manual (Page 9)

ENG-97D S TAND -A LONE ENMET Corporation
7
Calibration & Zeroing
Pushbutton Switch
Calibration Adapter
Gas Cylinder
Calibration Cup
Flow Control Valve
4.2 Automatic Zeroing
O XYGEN M ONITOR : Oxygen Monitor, 0 – 30% by volume, do not require the automatic zeroing step, proceed to section 4.3
automatic calibration.
T OXIC M ONITOR : If the air around the Monitor contains significant levels of the target gas or interference gases, the sensor must
be exposed to a source of fresh, clean air to perform an automatic zeroing procedure. Kits are available from ENMET
Corporation that includes a cylinder of 20.9% oxygen, free of contaminants. The recommended flow rate of air from a cylinder
is 0.5 liters per minute.
Expose the sensor to fresh clean air for at least 30 seconds. Press and release the Calibration & Zeroing Pushbutton Switch.
After the switch is released, if the signal from the sensor is within the established Zero (clean) range, the Monitor display is
forced to zero. If the sensor reading is too high or too low, zeroing will not take place.
N OTE : Under certain conditions, the display may be off 1 display unit.
If the Monitor does not read zero and continues to read more than several display units above zero, expose the sensor to clean
air from a cylinder of 20.9% oxygen for 2 minutes. After 2 minutes, press and release the Calibration & Zeroing Pushbutton
Switch again. If the display still does not zero, the sensor may need to be replaced.
4.3 Automatic Calibration
ENMET Corporation makes available a calibration kit that
contains the stipulated calibration gas and a calibration
adapter. With reactive gases it is imperative that the
proper regulator, tubing and calibration cover be used.
Failure to do so, may cause inaccurate and/or failed
calibrations. Contact your local distributor or
ENMET for
more information. See Table 2 for calibration gas values
and replacement cylinder part numbers.
Screw the regulator valve of the calibration adapter onto
the calibration gas cylinder, and open the flow control
valve. Put the cup over the sensor. See Figure 5.
After 1-3 minutes, when the display stops changing, press
the calibration switch. If the sensor output is within the
calibration range, the display changes to the value of the
contents of the calibration gas.
Example: If calibrating with 50 PPM CO, the display
changes to “0050”.
N OTE : Alternative calibration gas sources, such as
permeation tube or gas generator. Follow
instruction supplied with that equipment
N OTE : Under certain conditions, the display may be off
± 1 display unit, Hydrogen may be off ± 20 ppm.
Figure 5: Calibration with Gas
W ARNING : If at this point the display does not change, calibration has not been accomplished. Check the following:
♦
Be sure that the proper calibration adapter is being used. Reactive gases can be absorbed by standard tubing. Special non-
reactive tubing should be used for reactive gases.
ENMET calibration kits are supplied with appropriate tubing for the gas
in the kit.
♦
Be sure that the gas is not outdated. The shelf life or manufacture date is on the gas cylinder label.
♦
If sufficient fresh calibration gas is being used, try the calibration again. If the same result is obtained, the most probable
cause is a sensor with low output. Such a sensor is nearing the end of its useful life. Install a new sensor, and recalibrate.