Series-668B-D

Supported Applications

The Dwyer Series 668B/D Compact Differential Pressure Transmitters are designed to sense differential gage pressure and convert it into a proportional high-level analog output. These units support both unidirectional and bidirectional pressure ranges for air and non-conductive gases.

Operating Conditions & Performance

The series delivers an accuracy of ±0.8% FS with thermal effects specified as ±0.03% FS/°F (±0.054% FS/°C). The compensated range is from 40 to 170°F (4.4 to 77°C), while the operating temperature limits are 0 to 170°F (-18 to 77°C) and storage temperatures span -40 to 185°F (-40 to 85°C). The transmitters can withstand a pressure limit of 15 psig (1.0 bar).

Power requirements are 12-32 VDC. For the 4-20 mA output, load resistance ranges from 0 to 1000 Ω with maximum wire and receiver resistances defined by RL≤50(Vs-12). The enclosure is constructed of stainless steel and PC+ABS alloy rated UL 94 V-0.

Measurement Ranges

The series supports the following unidirectional ranges:

• 0 to 0.1 in w.c., 0 to 0.2 in w.c., 0 to 0.25 in w.c.
• 0 to 0.4 in w.c., 0 to 0.5 in w.c., 0 to 1 in w.c.
• 0 to 2.5 in w.c., 0 to 5 in w.c., 0 to 10 in w.c.
• 0 to 25 in w.c., 0 to 50 in w.c., 0 to 100 in w.c.

Bidirectional ranges include:

• 0 to ±0.1 in w.c., 0 to ±0.25 in w.c., 0 to ±0.5 in w.c.
• 0 to ±1 in w.c., 0 to ±2.5 in w.c., 0 to ±5 in w.c.
• 0 to ±10 in w.c., 0 to ±25 in w.c.

Tubing Recommendations

The Series 668B/D is designed for use with 3/16" I.D. push-on tubing. For optimal performance, the following tubing sizes are suggested based on length:

• 3/16" I.D. for lengths up to 80 feet (25 meters)
• 1/4" I.D. for lengths up to 250 feet (75 meters)
• 3/8" I.D. for lengths up to 720 feet (220 meters)

Configuration Options

The series offers configurable output signals, connection styles, and pressure ranges.

Output Signals

• 4-20 mA (2-wire)
• 0-10 VDC (3-wire)
• 0-5 VDC (3-wire)

Housing and Connections

The series is available in two housing configurations:

• 668B: Front connection style.
• 668D: Bottom connection style.

All models feature a 3/16" OD barbed brass process connection for 1/8" ID push-on tubing. Electrical connections are made via a terminal strip, and units include a protective terminal cover (replacement model A-TC available). Zero adjustment is accessible under the small terminal cover.

Key Product Differences

The primary distinction between models in this series lies in the connection orientation and specific range/output combinations. The 668B variant provides front connections, while the 668D variant offers bottom connections. Both share identical performance specifications including ±0.8% FS accuracy and a 15 psig (1.0 bar) pressure limit.

Model numbers follow the format 668--. For example, model 668B-08-1 indicates Series 668 with a front connection (B), range code 08 (0 to 25 in w.c.), and output code 1 (4-20 mA). An optional NIST traceable calibration certificate is available under order code NISTCAL-PT1.

Units are not field serviceable; if repair is needed, the unit should be returned. Field repair attempts may void the warranty.