Seametrics AO55 Blind Analog Transmitter

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.

Seametrics 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.

Seametrics AO55 Features

  • Pulse-to-analog converter
  • Current loop powered
  • Smooth output signal
  • Easy set-up
  • Durable


  • Telemetry/SCADA
  • Distributed control systems
  • Programmable controllers
  • Chart recording
  • Data logging


Power 24–36 Vdc
Temperature 32 ̊ to 130 ̊ F (0 ̊ to 55 ̊ C )
Input Open collector solid state sensor
Input Averaging 2–16 seconds (switch selectable)
Response Time 2–60 seconds; 90% of full scale (dependent on input averaging)
Frequency Minimum 10 Hz (@20mA)
Maximum 999.9 Hz
Setting 4 Rotary DIP switches
Output Proportional 4-20 mA
Environmental NEMA 4X, IP66

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Rudy Wiratama

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