RAEGuard 2 PID

Maintenance With the Enclosure in Place

This is the main argument for this detector, and it’s worth understanding what it saves.

An explosion proof enclosure in a Zone 1 area is only explosion proof while it’s closed. Opening one to adjust a setting or calibrate a sensor means a hot work permit, a gas clearance and a procedure, or shutting the area down. On a plant with a dozen detectors, that administrative load is the real cost of fixed VOC monitoring.

The RAEGuard 2 PID reduces it. A three key magnetic bar works through the housing, so calibration and parameter adjustment both happen with the explosion proof enclosure in place.

The DigiPID sensor module is designed to be easily removed for calibration or maintenance, so lamp cleaning, sensor replacement and bench calibration don’t mean working on the detector in place. Follow Honeywell’s procedure for removing the module in your area classification.

Reading Your Compound, Not Isobutylene

A photoionisation detector responds to any compound whose ionisation potential sits below the lamp energy, which covers several hundred substances. It’s calibrated against isobutylene and reports in isobutylene equivalent units, so a raw PID reading isn’t the concentration of the compound you’re actually measuring.

A correction factor converts one to the other, and the RAEGuard 2 PID holds more than 200 of them pre-programmed. Select the target compound, and the display reads that compound directly.

That matters more on a fixed installation than on a portable. Nobody is standing beside the detector with a correction factor table, so the number on the display, and the number the relays trip against, needs to be the real one.

Detected compounds include benzene, toluene, xylene, acetone, methyl ethyl ketone, vinyl chloride, phenol, dimethyl ether, ammonia and a broad range of solvents.

Keeping the Sensor Clean and the Reading Honest

This is a difference between fixed and portable PIDs that’s rarely explained.

A portable PID is zeroed in clean air before each use, so drift is corrected daily by the operator. A fixed PID can’t be. It sits in a classified area for months at a time, and anything that builds up on the lamp or sensor shows up as a shift in each reading and each alarm decision.

The RAEGuard 2 PID uses RAE Systems’ patented pump duty cycling, which helps keep the PID sensor clean. The pump cycles on and off within a 10 second period, and a lower duty cycle has a greater cleaning effect. Its digital smart sensor technology also supports environmental self adaptation.

Honeywell rates zero and span drift at ±10% of full scale per month, so periodic calibration is still part of the job. The magnetic key interface is what makes that calibration quick, with two point calibration as standard and three point calibration optional.

Three Ranges, and One Important Caveat

The caveat matters, and it’s easy to miss. On the 1 to 1,000 ppm range, correction factors and relays aren’t available. So that version reads in isobutylene equivalent only, and can’t drive an external alarm or a process action.

If the installation needs a relay output, or needs to read a specific compound, choose one of the other two ranges. Check this before ordering, rather than discovering it at commissioning.

Outputs and Integration

Three output paths run together.

An analogue 4 to 20 mA three wire output, for a conventional controller. RS-485 Modbus, for digital integration. And dry contact relays rated 30 V at 2 A, normally open or normally closed, one for high and low alarm, and another for fault.

The relays are what let the detector act rather than just report, triggering building alarms, ventilation or a process response directly.

Supply is 10 to 28 V DC, at under 5 W.

At the detector, there’s a 128 x 64 backlit graphic display, an LED status indicator for alarm and fault, and a local audible alarm. So anyone standing in front of it knows its state without going to a panel.

Diffusion or Pumped

The RAEGuard 2 PID can operate in diffusion or flow through mode, and the choice follows the installation.

In diffusion mode, the detector waits for gas to reach it, which suits general area monitoring where the release point isn’t known.

With the internal diaphragm pump, drawing up to 500 cc per minute, it samples continuously, which suits a specific point, a duct, an enclosure, or a location the gas won’t reach by itself.

Where It’s Used

Refineries and petrochemical plants. Power plants. Solvent recovery systems. Painting and coating operations. Wastewater treatment plants. Chemical manufacturing and storage. Tank farms and loading facilities. Benzene monitoring in classified areas. Any Zone 1 location where volatile organic compounds need continuous monitoring, rather than periodic survey.