Dwyer Photohelic 3000MR/3000MRS Differential Pressure Switch Gauge

Overview

The Dwyer Photohelic 3000MR is a differential pressure switch and gauge in one instrument. Dwyer Instruments combined a precise, highly repeatable pressure switch with a large analog dial built on the durable Magnehelic gauge movement, so operators can see the actual pressure while the unit controls a fan, damper, alarm or filter cleaning sequence. Two large knobs on the gauge face set the low and high limits, and the solid state design keeps the instrument compact and light. The family includes the 3000MR with electromechanical relays and the 3000MRS with solid state relays.

Seven Star LLC supplies the Dwyer Photohelic 3000MR and 3000MRS to HVAC contractors, OEM panel builders and plant maintenance teams in Oman and the GCC, with engineering support in Muscat. The instrument suits air and other non-combustible, non-corrosive gases in systems up to 25 psig, which covers most ventilation, clean room and pneumatic conveying duties found in Gulf facilities.

Working Principle

The indicating side of the Dwyer Photohelic 3000MR works like a Magnehelic gauge: differential pressure across a diaphragm deflects a calibrated range spring, and a magnet on the spring rotates a helix that carries the pointer. Because nothing in this path depends on electronics, the gauge reading is unaffected by switch operation and continues to show pressure accurately even if the 24 VDC supply is interrupted. The two set point indicators are positioned with the external knobs, and the electronics compare the pointer position with each set point to drive the low and high limit outputs.

On the 3000MR each set point drives one form C (SPDT) relay with gold over clad silver contacts rated 1.0 A at 30 VDC, 0.3 A at 110 VDC or 0.5 A at 125 VAC resistive, which makes them well suited to dry, low-energy circuits such as PLC inputs. On the 3000MRS each set point uses an SPST normally open solid state relay switching 20-280 VAC at up to 1.0 A, so the switch can cycle frequently without contact wear. Dwyer notes that the solid state design allows switching in high cycle rate applications without degradation.

Engineering Design of the Dwyer Photohelic 3000MR

The Dwyer Photohelic 3000MR has a 4-inch (101.6 mm) dial face and a 5-inch (127 mm) outside diameter, with an overall weight of about 816 g. Process connections on the Dwyer Photohelic 3000MR are 1/8 inch female NPT, duplicated on the side and back. Zero and range adjustments are made outside the gauge, so normal service does not require disassembly. The unit is designed for the diaphragm in a vertical position and can be flush mounted in a panel or surface mounted with the hardware supplied, which includes a mounting ring, snap ring, tubing adapters, pipe plugs and machine screws.

Electrical connection is through an 18-inch (46 cm) cable assembly, eight conductors on the 3000MR and six on the 3000MRS, with optional lengths to 100 feet (30.5 m). Power is 24 VDC regulated to plus or minus 10%. With the -SS option, the brushed 304 stainless steel bezel shares the installation diameter of a standard Magnehelic gauge, so a plant can upgrade an indicating gauge to a switch gauge in the same panel cutout.

Key Features

Engineers select the Dwyer Photohelic 3000MR and 3000MRS for the following reasons:

• One Dwyer Photohelic 3000MR provides both a readable analog differential pressure display and two independent control set points.
• The gauge reading is unaffected by switch operation and stays accurate during a power loss.
• Large external knobs on the face make low and high set point adjustment quick, and the -TAMP option locks them behind a spanner key.
• 3000MR relays are SPDT with gold over clad silver contacts, ideal for dry circuits and controller inputs.
• 3000MRS solid state relays handle high cycle rate switching of 20-280 VAC loads without contact wear.
• Zero and range adjustments are accessible from outside the case, avoiding disassembly in normal service.
• Accuracy is plus or minus 2% of full scale on most ranges, with -MP and -HP options for 35 psig and 80 psig ratings.
• The -SS stainless bezel matches the Magnehelic installation diameter, and a -WP weatherproof housing option is offered.

Industrial Applications

Dwyer highlights pneumatic conveying, air conditioning systems and clean rooms as typical applications. In practice the Dwyer Photohelic 3000MR is used to start a dust collector pulse cleaning cycle at a high filter differential and stop it at a low one, to alarm on loss of room pressurisation, to prove fan operation in air handling units, and to hold a pneumatic conveying line within its working pressure band. In Oman these duties appear in cement and gypsum plants, food and flour handling, hospital isolation rooms and data centre air handling across Muscat, Sohar and Salalah.

For packaging lines and process skids where a Dwyer Photohelic 3000MR would switch many times an hour, the solid state 3000MRS avoids relay wear, while the 3000MR is a natural fit where the outputs go straight to a PLC or BMS controller. Seven Star LLC supplies the Dwyer Photohelic 3000MR range with accessories such as the A-298 and A-370 mounting brackets and the A-600 R/C snubber recommended for inductive loads like solenoids and contactors, giving project teams across the GCC one source for the complete control point.

Technical Specifications

The Dwyer Photohelic 3000MR and 3000MRS specifications below are taken from the Dwyer catalogue datasheet.

Related instruments include the Dwyer Series MSX Magnesense differential pressure transmitter, the CCS 646GZE-7011 explosion-proof dual-snap pressure switch and the United Electric One Series 1XSWLL pressure switch.

How to Order

To order the Dwyer Photohelic 3000MR or 3000MRS, send Seven Star LLC a formal RFQ stating the range, relay type and any options, and our instrumentation division will confirm the exact model code. We provide engineering support in Muscat for customers in Oman and the GCC. Download the Dwyer Photohelic 3000MR datasheet from this page, or contact our team for mounting brackets, snubbers and calibration certificates.