Seametrics AO55 User Manual
Page 2
GENERAL INFORMATION, SPECIFICATIONS and INSTALLATION
The Seametrics AO55 is a blind (non-indicating) 4-20 mA
transmitter, designed for use with almost all Seametrics flow
sensors. It accepts a pulse frequency input from the flow
sensor, and converts this input into a continuous analog output
signal. Power for the transmitter is taken from the current
loop itself, so only two wires are required. The digital design
makes it possible to span the unit in the field without tools.
The frequency at which 20 mA is desired is entered on a set of
rotary switches, and an internal microcontroller automatically
scales all other values accordingly. An additional benefit of the
microcontroller is its ability to average inputs, for smoothing of
the output signal. The degree of averaging can be selected in
the field, from 2 to 16 seconds.
For maximum environmental protection, the electronic
components are encased in a special semi-flexible urethane
potting material. The housing is cast from aluminum and fuse-
coated. The clamshell housing is connected directly to the flow
sensor or, in the wall mount version, provided with mounting
feet.
The AO55 will operate on a relatively wide range of current loop
voltages, 24 to 36 Vdc. Lower voltages limit the load that can
be applied to the loop without distortion of the signal. (See
Load/Supply chart if there is a question regarding voltage vs.
load.) A built-in power regulator supplies the appropriate power
to the flow sensor.
Typical applications for this transmitter are telemetry (or
SCADA), distributed control systems, programmable controllers,
data logging, and chart recording.
Mounting.
The AO55M comes mounted on the flow sensor.
The AO55W wall mount comes with mounting feet and
requires four screws to attach it to any stable surface.
Connection.
On either style of housing, the upper portion
must be removed to make connections. Use a standard hex
wrench (5/32” or 4 mm) to loosen the screws, then remove
the upper half. The connections are made to terminal blocks
in the upper half, which contains the potted electronics.
Consult the Connections diagram before connecting to the
current loop. The only connections required on an AO55M
are the positive and negative loop connections. On an
AO55W, the sensor must also be connected, since it is
remote from the transmitter. Be careful to follow the color
coding of the flow sensor wires in order to establish the
correct polarity. Incorrect polarity can damage the sensor.
GENERAL INFORMATION
INSTALLATION
24 - 36 Vdc
32˚ - 130˚ F (0˚ - 55˚ C)
Open-collector solid state sensor
2 - 16 seconds (switch selectable)
2-60 seconds; 90% of full scale
(dependent on input averaging)
10 Hz (@20 mA)
999.9 Hz
4 Rotary DIP switches
Proportional 4-20 mA
Power
Temperature
Input
Input Averaging
Response Time
Frequency Minimum
Maximum
Setting
Output
SPECIFICATIONS*
Loop
Power
(Vdc)
Load Resistance (Ohms)
700
900
1100
1300
Load vs. Supply Voltage
Operating
Region
36
34
32
30
28
26
24
1500
*Specifications subject to change • Please consult our website for current
data (www.seametrics.com).