Seametrics AO55 Operating Manual

AO55

BLIND ANALOG TRANSMITTER
INSTRUCTIONS

A O 5 5 B L I N D A N A L O G T R A N S M I T T E R I N S T R U C T I O N S

GENERAL INFORMATION, SPECIFICATIONS and INSTALLATION

Loop
Power
(Vdc)

Load Resistance (Ohms)

700 900 1100 1300

Load vs. Supply Voltage

Ope r a t i n g

Reg i o n

36

34

32

30

28

26

24

1500

GENERAL INFORMATION 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 conver ts 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.

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.

Typical applications for this transmitter are telemetr y
(or SCADA), distributed control systems, programmable
controllers, data logging, and chart recording.

SPECIFICATIONS*

Power

Temperature

Input

Input Averaging

Response Time

Frequency Minimum

Maximum

Setting

Output

*Specifications subject to change • Please consult our website for current
data (www.seametrics.com).

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