Dwyer | Mercoid | WE Anderson | Flotect

Dwyer Series 645

Series 645 Wet/Wet Differential Pressure Transmitter

±0.25% Accuracy, Quick Response, 2-Wire Design

The Dwyer Series 645 Wet/Wet Differential Pressure Transmitters are designed for use with compatible gases and liquids which can be applied to both the pressure and reference ports. Quick response capacitance sensor delivers a 4 to 20 mA output signal proportional to differential pressure with ±.25% accuracy. The Series 645 transmitters are ideal for process control, filter condition monitoring, refrigeration equipment, pump speed control, HVAC equipment, and liquid level measurement. For ease of installation and maintenance, order optional 3-valve manifold assembly. Bleed ports allow for total elimination of air in the line and pressure cavities.


  • Service:Compatible gases or liquids on both pressure and reference sides.
  • Wetted Materials:17-4 PH stainless steel, 300 Series stainless steel, fluoroelastomer and silicone O-rings and bleed screw seals.
  • Accuracy:±0.25% FS (RSS).
  • Temperature Limits:Operating: 0 to 175°F (-22 to 80°C); Storage: -65 to 260°F (-54 to 126°C).
  • Pressure Limits:(High side) 1 to 5 psi: 20 x FS, 10 to 25 psi: 10 x FS, 50 psi: 5 x FS, 100 psi: 2.5 x FS; (low side) 2.5 x FS.
  • Thermal Effects:(includes zero and span) ±0.02% FS/°F, 30 to 150°F (-1 to 65°C).
  • Power Requirements:11 to 30 VDC.
  • Output Signal:4 to 20 mA, 2-wire.Zero and Span Adjustments:Adjustable, ±1 mA, non-interactive.
  • Response Time:30 to 50 ms.
  • Loop Resistance:0 to 1000Ω.
  • Electrical Connection:Barrier strip terminal block with conduit enclosure and .875″ (22 mm) diameter conduit opening.
  • Process Connection:1/4″-18 female NPT.
  • Housing:Stainless steel/aluminum, NEMA 4X (IP56).
  • Weight:14.4 oz (0.4 kg).
  • Agency Approvals:CE.

3-Valve Manifold Assembly

  • Manifold:Brass.
  • Valve Type:90° on/off.
  • Process Connection:1/4″-18 female NPT.


645-00-1 psidNo
645-0-3V0-1 psidYes
645-10-2 psidNo
645-1-3V0-2 psidYes
645-10±0.5 psidNo
645-10-3V±0.5 psidYes
645-11±1 psidNo
645-11-3V±1 psidYes
645-12±2.5 psidNo
645-12-3V±2.5 psidYes
645-13±5 psidNo
645-13-3V±5 psidYes
645-14±10 psidNo
645-14-3V±10 psidYes
645-15±25 psidNo
645-15-3V±25 psidYes
645-16±50 psidNo
645-16-3V±50 psidYes
645-20-5 psidNo
645-2-3V0-5 psidYes
645-30-10 psidNo
645-3-3V0-10 psidYes
645-40-25 psidNo
645-4-3V0-25 psidYes
645-50-50 psidNo
645-5-3V0-50 psidYes
645-60-100 psidNo
645-6-3V0-100 psidYes