Detcon PI-500 - Manual (Page 21)

d) Remove the zero air gas and cal adapter and allow the sensor 3-5 minutes to rest on ambient air. If there are residual
active VOC gases in the area, then the sensor will read higher than 0.0 ppm. If this is the case, then you can use
the Zero Offset feature to correct for this residual background amount.
e) Set the Zero Offset value according to the concentration value found following the zero calibration procedure. See
section 3.8.1.1 below.
3.8.1.1 Using the Zero Offset Feature
If it is determined that there is a constant and non-negligible amount of residual active VOC gases in the background
air, the Zero Offset feature can be used to correct for this.
a) Observe the sensor’s concentration reading on air after a zero air calibration procedure. This represents the back-
ground VOC contribution that you will be offsetting.
b) Access the Zero Offset software feature by applying the magnet to PGM2 for 15 seconds. Then use the magnet to
momentarily pass over PGM1 and advance to the “Set Zero Offset” menu. Then apply the magnet to PGM1 for 3
seconds to access this menu. The menu should now read as “Zero Offset = X.X. Use PGM1 to increment this
number up to your desired offset level. When the correct offset is set, apply the magnet to PGM1 for 3 seconds to
accept the value. Then apply the magnet to PGM2 for 3 seconds to return to Normal Operation.
c) When done correctly, the unit should read 0.0 when back in Normal Operation.
3.8.2 Calibration Procedure - Span
3.8.2.1 Set Response Factor
All span calibrations are recommended to be done with a calibration standard consisting of isobutylene in an air back-
ground. If your target gas is different than the isobutylene span gas, you will be required to apply the correct Response
Factor. Look up the Response Factor for your target gas in the Table shown in Section 3.2.3.
a) Enter the programming menu by holding the magnet stationary over “PGM2” for 15 seconds until the display reads
“View Program Status”, then withdraw the magnet. At this point you can scroll through the programming menu by
momentarily waving the magnet over “PGM1” or “PGM2”. The menu options are: View Program Status, Set Cal Level,
Set Response Factor, and Set Zero Offset. Scroll to the “Set Response Factor” selection.
b) Select “Set Response Factor” by holding the magnet over “PGM1” for 3 seconds until the display reads “RespFactor
= x.xx”, then withdraw the magnet. Use the magnet to make an adjustment to “PGM1” to increase or “PGM2” to
decrease the displayed value until the value is equal to the desired “Response Factor” value from Section 3.2.3.
NOTE: If you have multiple target gases, then select the target gas with the highest Response Factor from the Table.
This provides for the safest and earliest warning levels.
NOTE: If you are span calibrating with the target gas, instead of isobutylene, then the response factor should be left at 1.0
3.8.2.2 Span Calibration
NOTE: Isobutylene is the recommended calibration gas for this sensor.
CAUTION: Verif ication of the correct calibration gas level setting and calibration span gas concentration is
required before “span” calibration. These two numbers must be equal.
Span calibration consists of entering the calibration function and following the menu-displayed instructions. The dis-
play will ask for the application of span gas in a specif ic concentration. This concentration must be equal to the calibra-
tion gas level setting. The factory default setting for span gas concentration is 50% of range. In this instance, a span gas
containing a concentration equal to 50% of range is required. If a span gas containing 50% of range is not available,
other concentrations may be used as long as they fall within 10% to 90% of range. However, any alternate span gas con-
centration value must be programmed via the calibration gas level menu before proceeding with span calibration.
Follow the instructions below for span calibration.
PI-500 Toxic Gas Sensors PG.21