The Dwyer 605-20 Magnehelic® Differential Pressure Indicating Transmitter is a 0–20 in WC (approximately ~4980 Pa equivalent) unidirectional configuration of the Series 605 platform that combines the time-proven Magnehelic® mechanical dial gage with a 2-wire, 4–20 mA electronic transmitter in a single 4-inch instrument. The 605-20 measures positive pressure across the 0–20 in WC range and delivers both a local analog reading and a linear loop signal simultaneously, so a technician walking the equipment room reads the value directly off the dial while the building automation system receives the same measurement — no parallel gage + transmitter pair and no isolation amplifier between the local indicator and the loop.
The 605-20 delivers ±0.5% FS electrical accuracy and ±2% FS mechanical accuracy. Power for the 605-20 comes from any 10–35 VDC supply through the rear-mounted screw terminal block, and the 605-20 drops into 4-inch panel cutouts originally drilled for a standard Magnehelic® gage — ordering with the optional -SS stainless bezel makes a one-for-one field upgrade without rework, so legacy gage installations get a BAS-compatible signal without a panel re-cut.
Filter monitoring across HVAC air handler banks, duct static pressure on supply and return trunks, building pressurization in light-industrial spaces, cleanroom pressure indication with BAS signal to the control room, and field upgrade of legacy Magnehelic® gage panels to a 4–20 mA loop.
Key Features
The 605-20 puts a Magnehelic® analog dial and a calibrated 2-wire 4–20 mA transmitter into the same 4-inch instrument, so the 605-20 gives a maintenance technician a direct visual reading while the controller upstairs sees the same measurement as a loop signal.
Inside the 605-20 is the same magnetically-linked diaphragm-and-helix sensing mechanism that has driven the Magnehelic® gage line for decades — quick response and ±1% FS/year stability without recalibration drift.
The 605-20 falls in the tightest accuracy class in the Series 605 family at ±0.5% FS — sharp enough to drive trending and alarms on this 0–20 in WC range without the noise floor of lower-class transmitters.
The 605-20 is a true 2-wire transmitter powered by any 10–35 VDC supply through the rear screw-terminal block, with a maximum 1250 Ω loop resistance — making the 605-20 a drop-in fit for nearly any BAS or PLC current-loop input without isolation amplifiers.
Ordered with the optional -SS brushed-stainless bezel, the 605-20 matches the installation diameter of a standard Magnehelic® gage — existing 4-inch panel cutouts accept the 605-20 directly, so gage-only panels can be upgraded to a 4–20 mA signal point without re-cutting sheet metal.
Zero and span on the 605-20 are set with protected potentiometers driven by a supplied spanner-style key — not exposed knobs — so a verified 605-20 calibration stays put even in shared mechanical rooms with foot traffic.
Technical Specifications
| Specification | Value |
|---|---|
| Manufacturer Part Number | 605-20 |
| Series | Dwyer Series 605 Magnehelic® Indicating Transmitter |
| Pressure Range | 0–20 in WC (approximately ~4980 Pa) |
| Direction | Unidirectional |
| Service | Air and non-combustible, compatible gases |
| Electrical Accuracy | ±0.5% FS (includes linearity, hysteresis, repeatability) |
| Mechanical Accuracy | ±2% FS |
| Long-Term Stability | ±1% FS/year |
| Maximum Pressure | 11 psi (75.8 kPa) |
| Operating Temperature | 20 to 120 °F (-6.67 to 48.9 °C) |
| Compensated Temperature Range | 32 to 120 °F (0 to 48.9 °C) |
| Thermal Effect | ±0.025% FS/°F (±0.045% FS/°C) |
| Power Requirements | 10–35 VDC (2-wire) |
| Output Signal | 4–20 mA |
| Loop Resistance | 0–1250 Ω max |
| Current Consumption | 38 mA max |
| Zero & Span Adjustment | Protected potentiometers (spanner key supplied) |
| Electrical Connections | Screw terminal block (rear) |
| Process Connections | 1/8 in female NPT (high and low) |
| Mounting | Panel mount or surface mount |
| Mounting Orientation | Diaphragm vertical (required for stated accuracy) |
| Dial Face Size | 4 in (101.6 mm) |
| Outside Diameter | 5 in (127 mm); 4-3/4 in (120.7 mm) with -SS bezel |
| Depth | 2-11/16 in (68.3 mm); 2-21/32 in (67.5 mm) with -SS bezel |
| Weight | 1 lb 12.6 oz (811 g) |
| Compliance | CE |
| Options Available | -SS (304 brushed stainless steel bezel), -NIST (traceable calibration certificate) |
What’s In the Box
- Dwyer Series 605 Magnehelic® indicating transmitter (605-20)
- Mounting ring and split snap ring for panel mounting
- (4) 6-32 x 1-1/4 in screws for panel mounting
- (3) 6-32 x 5/16 in screws for surface mounting
- (2) Tubing-to-1/8 in NPT adapters
- (2) 1/8 in NPT pipe plugs (for unused pressure ports)
- Spanner-style adjustment key (for protected zero/span potentiometers)
Documentation
Frequently Asked Questions
The 605-20 is a unidirectional indicating transmitter with a 0–20 in WC range. The 605-20 reads positive pressure applied to the HI port relative to the LOW port; both the analog dial and the 4–20 mA loop signal scale linearly across that span.
For the rated accuracy, yes — the 605-20 is factory-calibrated with the diaphragm in the vertical position and should be installed face-vertical. Non-vertical orientation will shift the zero and degrade the published accuracy of the 605-20; consult Dwyer if a non-standard orientation is required.
The 605-20 outputs a 2-wire 4–20 mA current signal linearly proportional to the 0–20 in WC range, with 4 mA at zero (or the negative end on bidirectional models) and 20 mA at full scale. Maximum loop resistance is 1250 Ω at 35 VDC.
Yes — ordering the 605-20 with the optional -SS (304 brushed stainless steel) bezel makes the installation diameter compatible with the standard Magnehelic® gage cutout, so an existing 4-inch panel hole accepts the 605-20 directly. This is the intended field-upgrade path for gage-only panels that need to feed a 4–20 mA loop to the BAS.
Any 10–35 VDC supply with at least 40 mA capacity per 605-20. The 605-20 is a 2-wire transmitter and is not designed for AC voltage operation — applying AC will cause permanent damage not covered by warranty.
Yes — a single DC supply can power several 605-20 transmitters in parallel as long as the supply has enough current. Minimum required current is the number of 605-20 units multiplied by 20 mA.
Yes — insert a 250 Ω resistor (commonly 249 Ω 1/2 W ±1% metal film) in series with the 605-20 current loop, in parallel with the receiver input at the panel end. The voltage drop across that resistor converts the 4–20 mA loop into a 1–5 V input.
The 605-20 ships factory-calibrated for 4 mA at zero and 20 mA at full scale. To re-verify: insert a milliammeter in series with the loop, vent both ports and set the dial zero with the slotted screw at center-bottom, apply 20 in WC to the HI port, and use the supplied spanner key on the protected SPAN potentiometer for 20 mA then on ZERO for 4 mA. The two controls are slightly interactive on the 605-20 — iterate two or three times.
- Brand:
- Dwyer
- Series:
- 605 Magnehelic
- Product Type:
- Indicating Transmitter
- Pressure Range Class:
- Medium (10–50 in WC)
- Pressure Range:
- 0-20 in WC
- Direction:
- Unidirectional
- Output Signal:
- 4-20 mA
- Display:
- Analog Dial
- Accuracy Class:
- High (0.5% FS or better)
- Mounting:
- Panel/Surface
- Probe:
- No Probe
