Series-645

Supported Applications

The Dwyer Series 645 Wet/Wet Differential Pressure Transmitters are designed for measuring differential pressure in systems where compatible gases or liquids can be applied to both the high and low (reference) ports. The series utilizes a fast response capacitance sensor with an isolation system that transmits diaphragm motion from the line pressure environment to a dry enclosure, enabling accurate measurement even when liquid is present on both sides.

Documented applications include:

• Process control
• Filter condition monitoring
• Refrigeration equipment
• Pump speed control
• HVAC equipment
• Liquid level measurement

Operating Conditions & Performance

The Series 645 delivers a ±0.25% FS (RSS) accuracy with non-interactive zero and span adjustments of approximately ±1 mA. The transmitter features a response time of 30 to 50 ms and operates within an ambient temperature range of 0 to 175°F (-22 to 80°C). Storage temperatures are rated from -65 to 260°F (-54 to 126°C).

Thermal effects, including zero and span drift, are specified as ±0.02% FS/°F within the range of 30 to 150°F (-1 to 65°C). The unit is powered by a supply voltage of 11-30 VDC with a loop resistance capability of 0 to 1000 Ω.

Pressure limits vary by measurement range. For the high side, maximum overload pressure is defined as: 20 x FS for ranges up to 5 psi; 10 x FS for 10 to 25 psi; 5 x FS for 50 psi; and 2.5 x FS for 100 psi. The low side limit is rated at 2.5 x FS.

Configuration Options

The series offers a range of differential pressure spans from 0 to 1 psid up to 0 to 100 psid, available in standard configurations and with optional manifold assemblies. The transmitter housing is constructed of stainless steel/aluminum with an enclosure rating of NEMA 4X (IP56).

Key configurable features and specifications include:

• Process Connection: 1/4"-18 female NPT
• Electrical Connection: Barrier strip terminal block with conduit enclosure featuring a .875" (22 mm) diameter opening for 1/2" ID conduit.
• Wetted Materials: 17-4 PH stainless steel, 300 Series stainless steel, fluoroelastomer and silicone O-rings, and bleed screw seals.
• Bleed Ports: Three bleed screws (two for the low pressure port, one for the high) allow for air elimination from lines and cavities.

An optional 3-valve manifold assembly is available to facilitate installation and maintenance. This accessory includes a brass manifold with 90° on/off valves and matches the 1/4"-18 female NPT process connection. A NIST traceable calibration certificate (order code: NISTCAL-PT1) is also offered.

Key Product Differences

The Series 645 model numbering indicates the specific differential pressure range, such as Model 645-0 for 0 to 1 psid through Model 645-6 for 0 to 100 psid. Specific SKUs ending in "-3V" denote units supplied with the optional 3-valve manifold assembly.

While the standard unit provides a barrier strip terminal block, models configured with the 3-valve option include the brass manifold and valve set integrated into the order code designation. All variants maintain the same core performance specifications regarding accuracy, response time, and environmental ratings as defined in the series data sheet.