Honeywell RAEGuard 2 PID Installation Guide

Technical Note

Installation and Maintenance
of a RAEGuard 2 PID

INTRODUCTION

The Honeywell® RAEGuard 2 PID is a fixed photoionization detector (PID) that measures
a broad range of Volatile Organic Compounds (VOCs). The RAEGuard 2 PID monitor
operates in flow through mode. Housed in an explosion-proof stainless-steel enclosure,
the RAEGuard 2 PID can be used in most environments, including hazardous
environment applications for measuring toxic gases. Therefore, correct installation and
maintenance is required to ensure effectiveness as a VOC monitor.

This technical note describes guidelines for installation, commissioning, testing,
calibration and maintenance of the RAEGuard 2 PID and the factors that need to be
considered.

INSTALLATION

This instrument can be installed as a stand-alone unit or as part of a multi-point VOC
monitoring system.

Preface

1998-1001 Rev 1 11/16

It is vital to understand the gas and conditions to be measured. Many factors can impact the
performance of an active sampling system, including dust, water condensation, gas
condensation, and pressure within a duct.

Dust

Unless the particle size is less than 1 micron, the only impact on the performance is the filter
replacement interval.

Water condensation

The RAEGuard 2 PID system is able to operate within a relative humidity range of 0 to 95%,
non-condensing, without distortion of the actual VOC concentration reading. Nevertheless,
water vapors are very often present within VOC samples, especially in many duct sampling
applications. The sample temperature very often is high enough, and is higher than at the
measurement point. On the way from the sampling point to the instrument, the sample gas
is cooling. As temperature decreases, relative humidity (RH) of the water vapors in the VOC
samples increases and may reach 100% or the dew point. If the temperature at the measuring
point is lower than the dew point, water vapor may condense in the tubing, on the PID lamp,
and on the PID electrodes. The amount of condensed water may be significant and may affect
the accuracy of the measurement.

For example

If the sampling temperature is 122° F (50° C) and 40% RH, and at the measurement point the
temperature is 77° F (25° C), about 10 g of water may condense from 1m3 of the sampling air
within two (2) to three (3) days.

1

Technical Note

Installation and Maintenance
of a RAEGuard 2 PID

Presence of water must be considered at the lowest ambient temperature and the highest RH
at the highest temperature in the sample line. This calculation must be performed when
sampling from ducts (additional sampling equipment may be required). Honeywell
recommends using a water-collecting filter; housing part number 490-0163-000 and filter
replacement 490-0164-010 (pack of 10).

Figure 1. Water-collecting filter

Note: Filter housing and filter replacement elements are currently available only in North
America. Contact Honeywell for more information. The filter is installed between the sample
source and the instrument, at a location where the temperature does not exceed the
instrument’s rated operating temperature.

1998-1001 Rev 1 11/16

Target and background gases condensation

Many toxic gases have a low vapor pressure. Therefore, gas may become a liquid or a crystal
even at very low concentrations if the temperature at the measurement point is lower than
at the sampling point. This factor must be considered before selecting an active sampling
system.

The following example illustrates the fundamentals of the vapor pressure issue:

Phenol

The Honeywell® RAEGuard 2 PID can be used in phenol factories all over the world. Phenol
can crystallize from the gas phase to the solid phase when its vapor pressure in the gas state
is higher than that of the sublimation vapor of the solid phenol. This process depends greatly
on the temperature variations, since vapor pressures depend on them.

The approximate maximum Phenol gas concentrations in air at different temperatures are as
follows:

• At 122° F (50° C): The maximum concentration of phenol is around 3600 ppm.

• At 77° F (25° C): The maximum concentration of phenol is around 440 ppm.

Pressure

Until pressure variation is within a specified range of 90 to 110 kPa, a monitoring instrument
gives a correct reading. Make sure the pressure in the sampling duct does not exceed these
values. Slightly exceeding them is acceptable, but the reading may be distorted. That
distortion does not relate to the PID itself, which is rather stable in terms of pressure variation,
but it does relate to sampling gas density variation.

2