Dwyer 668 User Manual

Bulletin A-30-668

Ø

5/32 [3.97]
MOUNTING HOLE
T

YP 2 PLACES

3-5/32
[

80.16]

3/8
[

9.53]

1-7/8
[

47.63]

6-32 SCREW
W

/TERMINAL WASHER

2-3/4
[

69.85]

1

[

25.40]

3

/16 [4.76]

F

ITTING

3-1/2
[

88.90]

1-41/64

[41.67]

LOW

HIGH

_
COM

+
EXCOUT

Series 668 Differential Pressure Transmitter

Specifications - Installation and Operating Instructions

Our low cost Series 668 Differential Pressure Transmitter is capable of
measuring low pressures with a ±1% accuracy ideally suited for proper
building pressurization and air flow control. Transmitters can withstand
up to 10 psig overpressure with no damage to the unit. Variable capac­itance sensor design provides excellent sensitivity and long-term stabil­ity. Compact, lightweight design makes installation simple and easy.
Units also feature reverse-polarity protection.

INSTALLATION
Mounting

The 668 Series is designed for mounting in either a switch box or by
using the two (2) holes that are provided on the housing. Optimum per­formance is obtained by isolating the instrument from vibration and pro­viding relatively clean, dry ambient air to the pressure ports. In most
cases, preferred installation is with the baseplate mounted vertically and
located on a relatively flat surface in a junction box or attached to a near­by beam.

CAUTION: The axis most sensitive to vibration is the one perpendicular
to the mounting base. Avoid mounting with maximum vibration along the
axis.

Pressure Fitting

Two (2) 3/16˝ O.D. pressure fittings are supplied for pressure connec­tion with 1/4˝ push-on tubing. Both the positive (high) pressure port and
the reference (low) pressure port are located on the top face of the unit,
labeled High and Low respectively. For best results (shortest response
times), 3/16˝ I.D. tubing is suggested for tubing lengths up to 100 feet
long, 1/4˝ I.D. for tubing lengths up to 300 feet, and 3/8˝ I.D. for tubing
lengths up to 900 feet.

SPECIFICATIONS
Service: Air and non-conductive gases.
Accuracy: ±1% of full scale (RSS)

(includes non-linearity, hysteresis, and non-repeatability).

Temperature Limits:

Operating: 0 to 150°F (-18 to 65°C);
Storage: -40 to 185°F (-40 to 85°C).

Pressure Limits: 10 psig (0.7 kg/cm2).
Compensated Temperature Range: 0 to 150°F (-18 to 65°C).
Thermal Effects: 0.033% FS/°F (0.018% FS/°C).
Supply Voltage: 12-30 VDC.
Output: 4 to 20 mA, 2-wire.
Zero and Span Adjust: ±1 mA, non-interactive.
Response Time: <60 msec.
Loop Resistance: 0-800 ohms.
Electrical Connection: Terminal strip.
Pressure Connection: 3/16 9 O.D. fitting for 1/49 I.D. tubing.
Housing: Fire retardant glass filled polyester.
Weight: 3 oz (85 g).
Agency Approvals: CE.

Models & Ranges

Model

Number*

668-1
668-2
668-3
668-4

Range

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

Model

Number*

668-5
668-6
668-7
668-8
668-9

Range

0 to 5.0 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.

Bi-Directional Models

Model

Number*

668-10
668-11
668-12

DWYER INSTRUMENTS, INC.

P.O. Box 373 • Michigan City, IN 46360, U.S.A. Fax: [phone] e-mail: [e-mail]

668-13

*Also available with optional conduit cover. To order add “C” to part
number, i.e. 668C-1. Consult factory for additional information.

Phone: [phone] www.dwyer-inst.com

Range

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

Model

Number*

668-14
668-15
668-16
668-17
668-18

Range

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.

ELECTRICAL CONNECTIONS

The Series 668 Differential Pressure Transmitter is a loop-powered 4 to
20 mA current output unit. The current flows into +EXC. terminal and
returns back to the power supply through the -EXC. terminal. the power
supply must be a DC voltage source with a voltage range between 12
and 30 VDC measured between terminal +EXC. and -EXC.

The unit is calibrated at the factory using a 250 ohm load at 28 VDC.

Span Adjustment (Complete the zero adjustment before setting
span)

Span on full scale output adjustments should only be performed by
using an accurate pressure standard (electronic manometer, digital
pressure gage, etc.) with at least comparable accuracy to the 668 series
(<±1% full scale). With full scale pressure applied to the high pressure
port (reference port open to atmosphere) adjust span to achieve 20 mA
output.

Notes:
Minimum Supply Voltage (VDC) = 12 + 0.02 x (resistance of receiver
plus line).

Maximum Supply Voltage (VDC) = 30 + 0.004 x (resistance of receiver
plus line).

CALIBRATION

The 668 series is factory calibrated and should require no field adjust­ment. However, both zero and span adjustments are provided.
Whenever possible, any zero and/or span offsets should be corrected by
software adjustment in the user’s control system. Use the zero and span
adjustments on the 668 Series only if absolutely necessary. The 668
series is calibrated in the vertical position at the factory. For use in other
orientations, position the unit and follow the zero adjustment procedure
listed below. Pressure ranges are fixed and cannot be changed in the
field.

Zero Adjustment

While monitoring the current output with both pressure ports open to
atmosphere, the zero may be adjusted. For unidirectional pressure
ranges, turn the zero adjustment screw until a reading of 4 mA (±0.15
mA) is achieved.

Example 1: Unidirectional pressure range of 0 to 1˝ w.c. Apply 1.00˝ w.c.,
adjust span to 20 mA.

Notes: The input is reverse-voltage protected. The output is internally
protected against damage is shorted to ground. Recheck all connections
before applying power.

MAINTENANCE

After final installation of the Series 668 Differential Pressure Transmitter,
no routine maintenance is required. A periodic check of system calibra­tion is recommended. These devices are not field repairable and should
be returned if recalibration or other service is required. Contact cus­tomer service to obtain an RGA number. Please include a clear descrip­tion of the problem plus any application information available.

©Copyright 2014 Dwyer Instruments, Inc. Printed in U.S.A. 5/14 FR# R8-443095-00 Rev. 2

DWYER INSTRUMENTS, INC.

Phone: [phone] www.dwyer-inst.com

P.O. Box 373 • Michigan City, IN 46360, U.S.A. Fax: [phone] e-mail: [e-mail]