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to the CGI inlet or blanketing the CGI detector element (element) with an atmosphere from a calibration gas cylinder. The CGI readout is then set to that value using whatever device (set- screw, etc.) the CGI possesses to adjust the instrument to the calibration value. V Depending on which calibration gas is used for a particular CGI, the instrument manufacturer normally provides data on the relative response of other organic solvents relative to the "factory"calibration. For example, a CGI calibrated for methane could be used rto measure benzene, if the manufacturer supplies a relative response curve for that compound. Of course, most solvent measurements are of mixtures and it is often difficult to accurately assess these mixtures. This is one reason that CGI's are normally set to alarm at conservative levels (usually 20 percent of the LEL of the organic compound chosen as the calibration standard). 510.3.2 Oxygen Meter The meter should be allowed to warm up for a few minutes prior to calibration. A cylinder of calibration gas (typically containing 17 percent OZ and 25,000 ppm methane). is attached to the meter inlet. (In the case of passive air flow instruments, a hood or cover is placed over the V detectors and this in turn is connected to the calibration gas.) Calibration to 21 percent of OZ may also be performed using ambient air. V The calibration gas is turned on and is allowed to stabilize for 15 to 30 seconds. The meters are then adjusted (following manufacturer's instructions) to proper calibration. This usually involves adjusting a set screw at the base of the meter. The instrument should then be rechecked for proper return to zero. 510.3.3 HNU Photoionization Detector (Model PI 101) The instrument is turned to the battery check position first. Assuming proper charge, the main V control switch is set to the standby position using the zero knob. The instrument is then allowed to warn up for about five minutes in the standby mode. The calibration gas (usually isobutylene from the HNU •factory) is attached per the calibration test set up diagram (attached). The proper range-setting is selected (usually 0 to 200 ppm) and the calibration gas turned on. �. Revised: 11/93 HS-510-2 Woodward-Clyde