The 668B/D is a compact differential pressure transmitter that measures extremely low pressure ranges down to 0.1" w.c. It features current or voltage outputs, front or bottom pressure connections, and protection from overpressure and incorrect wiring. It is designed for HVAC applications such as measuring pressure differences in clean rooms, duct static pressure, and monitoring variable air volume systems and air filters.

1. Series 668B & 668D
Compact Differential Pressure Transmitter
T h e m a t e r i a l s i n c l u d e d i n t h i s c o m p i l a t i o n a r e f o r t h e u s e o f D w y e r I n s t r u m e n t s , I n c . p o t e n t i a l c u s t o m e r s
a n d c u r r e n t e m p l o y e e s a s a r e s o u r c e o n l y . T h e y m a y n o t b e r e p r o d u c e d , p u b l i s h e d , o r t r a n s m i t t e d
e l e c t r o n i c a l l y f o r c o m m e r c i a l p u r p o s e s . F u r t h e r m o r e , t h e C o m p a n y ’ s n a m e , l i k e n e s s , p r o d u c t n a m e s , a n d
l o g o s , i n c l u d e d w i t h i n t h e s e c o m p i l a t i o n s m a y n o t b e u s e d w i t h o u t s p e c i f i c , w r i t t e n p r i o r p e r m i s s i o n f r o m
D w y e r I n s t r u m e n t s , I n c .
© C o p y r i g h t 2 0 1 6 D w y e r I n s t r u m e n t s , I n c .

2. Summary
• New 668B/D unit features
• Model dependent front or bottom pressure
connections
• Protection from incorrect wiring & 15 psi overpressure
• Model dependent current or voltage outputs
• Terminal cover included but replacement cover is
available and separately orderable.
668B
668D

3. Summary
668B/D
Pressure
Ranges
Accuracy
Pressure
Limit
Outputs
• 668B/D: Down to 0.1” w.c.
• 668B/D: 0.8% FS
• 668B/D: 15 psi Overpressure
• 668B/D: 4-20 mA, 0-5 VDC, 0-10 VDC

4. Model Chart
Model Chart
Example 668 X -XX -X 668B-05-2
Series 668 Compact Differential Pressure Transmitter
Connection
B Front
D Bottom
Unidirectional
Pressure Ranges
01 0 to 0.1 in w.c.
21 0 to 2 in w.c.
02 0 to 0.25 in w.c.
22 0 to 0.4 in w.c.
03 0 to 0.5 in w.c.
04 0 to 1 in w.c.
05 0 to 2.5 in w.c.
06 0 to 5 in w.c.
07 0 to 10 in w.c.
08 0 to 25 in w.c.
09 0 to 50 in w.c.
10 0 to 100 in w.c.
Bi-Directional
Pressure Ranges
12 0 to ±0.1 in w.c.
13 0 to ±0.25 in w.c.
14 0 to ±0.5 in w.c.
15 0 to ±1 in w.c.
16 0 to ±2.5 in w.c.
17 0 to ±5 in w.c.
18 0 to ±10 in w.c.
19 0 to ±25 in w.c
Output
1 4 to 20 mA
2 0 to 10 VDC
3 0 to 5 VDC

5. • Extremely Low Pressure Ranges
– Uni-Directional Ranges Down to 0.1” w.c.
– Bi-Directional Ranges Down to ±0.1” w.c.
• Current & Voltage Output Models
Available
– 4 to 20 mA
– 0-5 VDC
– 0-10 VDC
668B/D Features & Benefits

6. • Compact & Lightweight design makes
installation simple & easy
– Units are protected against incorrect wiring &
include a protective terminal cover
– Pressure ports designed to be used with push-on
tubing with:
• 3/8” ID for lengths up to 80’ (25 m)
• 1/4” ID for lengths up to 250’ (75 m)
• 1/2” ID for lengths up to 720’ (220 m)
668B/D Features & Benefits

7. • HVAC Markets
– Primary use: Accurately measure
differential pressure & send analog
signal to a controller or PLC
Applications:
• Measuring Pressure Differences
in Clean Rooms & Isolation
Rooms
• Measuring Duct Static Pressure
• Measuring Pressure in Variable
Air Volume Systems
• Filter Monitoring
Series 668B/D Markets

8. • The 668B/D can be used to measure
the pressure difference between
two rooms or a room & the hallway
• Can be used to monitor a positive
pressure or as an open door/broken
seal alarm
Clean Rooms & Isolation Rooms
Series 668B/D Applications
• Other Dwyer products to consider:
– Static Pressure Accessories
– CO2, Humidity, Temperature Transmitters
(CDTA, CDTR)
– Temperature Sensors (TE)
– Fume Hood Monitor (670)
– Differential Pressure Switches (ADPS,
EDPS)

9. • The 668B/D can be used to
measure the velocity & static
pressure in a duct to determine
the air velocity
• The 668B/D can also be used
to monitor the static pressure
in a duct so that it does not
exceed design constraints
Series 668B/D Applications
Duct Static Pressure
• Other Dwyer products to
consider:
– Static Pressure Accessories
– AQTIA (UHH2, AP2, RP2, VP2, WDPM)
– Pitot Tubes

10. • The 668B/D is used to measure
the velocity pressure delivered
to each zone to give feedback
to the PLC/VFD
• The 668B/D is used to measure
the pressure drop across a
heating or cooling coil
Series 668B/D Applications
Variable Air Volume
• Other Dwyer products to
consider:
– Static Pressure Accessories
– Series TE VAV Temperature Sensor
– Relative Humidity Transmitters (RHP)
– CO2 Transmitters (CDT)
– Combo Units (CDTA, CDTR)

11. • The 668B/D can be used to
measure the pressure drop
across air filters
• As the filter accumulates
debris, the pressure drop will
increase
Series 668B/D Applications
Filter Monitoring
• Other Dwyer products to
consider:
– Static Pressure Accessories
– DP Switches (ADPS, EDPS, 1800,
1900)
– Control Enclosures (CSE, SSE)
– Manometers (MARK II 25)
– DP Gauges (Magnehelic)

12. 668B Specifications
SPECIFICATIONS
Services: Air & Non-Conductive Gases
Accuracy: ±0.8% FS
Temperature Limits:
Operating: 0 to 170° F (-18° to 77° C)
Storage: -40° to 185° F (-40° to 85° C)
Compensated
Temperature Range:
40° to 170°F (4.4° to 77°C).
Pressure Limits: 15 psig (1 bar)
Thermal Effect: ±0.03% FS/°F (±0.054% FS/°C)
Power Requirement: 12 to 32 VDC
Output: 4-20 mA, 0-5 VDC, or 0-10 VDC
Zero Adjustment: Accessible under the small terminal cover
Loop Resistance: RL ≥ 50*(Vs – 12)
Electrical Connections: Terminal Strip
Process Connections: 3/16 ̋OD barbed brass for 1/8 ̋ ID push-on tubing
Process Connection
Location:
Front
Weight: 4.0 oz (113 g)
Enclosure: Stainless steel and PC+ABS alloy, UL 94 V-0 rated
Agency Approvals: CE

13. 668B Specifications
SPECIFICATIONS
Services: Air & Non-Conductive Gases
Accuracy: ±0.8% FS
Temperature Limits:
Operating: 0 to 170° F (-18° to 77° C)
Storage: -40° to 185° F (-40° to 85° C)
Compensated
Temperature Range:
40° to 170°F (4.4° to 77°C).
Pressure Limits: 15 psig (1 bar)
Thermal Effect: ±0.03% FS/°F (±0.054% FS/°C)
Power Requirement: 12 to 32 VDC
Output: 4-20 mA, 0-5 VDC, or 0-10 VDC
Zero Adjustment: Accessible under the small terminal cover
Loop Resistance: RL ≥ 50*(Vs – 12)
Electrical Connections: Terminal Strip
Process Connections: 3/16 ̋OD barbed brass for 1/8 ̋ ID push-on tubing
Process Connection
Location:
Bottom
Weight: 4.0 oz (113 g)
Enclosure: Stainless steel and PC+ABS alloy, UL 94 V-0 rated
Agency Approvals: CE