Series-685

Supported Applications

The Dwyer Series 685 is a differential pressure and vacuum transmitter designed for building automation systems, clean room monitoring, valve and flap control, filter monitoring, and air flow control. The device measures service media consisting of air and non-corrosive gases.

Operating Conditions & Performance

The Series 685 utilizes a piezoresistive pressure sensor with an accuracy specification of ≤ ±0.5% RSS (BFSL), ±1 Pa, based on measurements at 73°F (23°C). Long-term stability is rated at ≤ ±1% FS per year in the manual and ≤ ±1% RSS per year in the datasheet; both values are documented sources for this series.

Operating ambient temperature limits range from -4 to 158°F (-20 to 70°C), with humidity tolerance up to 0 to 95% RH, non-condensing. The response time is configurable via a jumper: 1 s (default) or 200 ms (user selectable). Pressure ratings vary by model; for example, the 685-03 through 685-13 models list an over-pressure limit of 85 kPa and burst pressure of 135 kPa.

Configuration Options

The series offers a broad selection of measurement ranges to accommodate specific process needs. Available differential pressure spans include:

• Inches water column: 0 to 1 in w.c., 0 to 2 in w.c., 0 to 3 in w.c., 0 to 5 in w.c., 0 to 10 in w.c., 0 to 15 in w.c., 0 to 20 in w.c., 0 to 25 in w.c., and 0 to 40 in w.c.
• Pascals: 250 Pa, 750 Pa, 1250 Pa, 2500 Pa, and 5000 Pa.

Electrical output options include a 2-wire configuration providing 4-20 mA or a 3-wire configuration providing 0-10 V. Power supply requirements are 18-30 VDC for the 2-wire version and 18-30 VAC/DC for the 3-wire version.

Physical construction features an ABS housing with dimensions of Ø 66 x 28 mm, weighing 1.6 oz (46 g). The unit carries CE and UKCA compliance marks and is rated IP54. Process connection utilizes a 6 mm hose interface. Electrical connections are available via spring connector for cable and leads up to 1.5 mm² or screw fastening with sheet metal screws, depending on the specific variant documentation.

Additional options include an adjustable pressure range, a single button zero function, and factory restore capability via long button press. A DIN rail adapter kit (Model A-685-DIN) is available for mounting flexibility.

Key Product Differences

The Series 685 model numbering distinguishes pressure ranges and output types. Models ending in -V indicate the 0-10 V output signal, while models without this suffix default to the 4-20 mA output. Specific range codes correspond directly to measurement spans: for instance, code "-3" denotes a 0 to 5 in w.c. range with an over-pressure of 85 kPa and burst pressure of 135 kPa.

Thermal effects vary by model; the additional error with temperature is ±0.7% FS/10°C for models 685-00(-V) and 685-09(-V), while other ranges such as 685-03 through 685-13 list an additional error of ±0.3% FS/10°C.