AO55 Analog Transmitter with out display

The Seametrics AO55 blind analog transmitter is a non-indicating 4-20 mA transmitter designed for use with almost all Seametrics flow sensors. The AO55 accepts a pulse frequency input from the flow sensor and converts this input into a continuous analog output signal. Power for the AO55 is taken from the current loop itself so only two wires are required.

The digital design of the Seametrics AO55 blind analog transmitter makes it possible to span the unit in the field without tools. The frequency at which 20mA 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 AO55 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 of the AO55 transmitter are encased in a special semi-flexible urethane potting material. The housing is cast from aluminum and fuse-coated. The AO55’s 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, 12 to 36 VDC. However, lower voltages limit the load that can be applied to the loop without distortion of the signal. A built-in power regulator supplies the appropriate power to the flow sensor. Typical applications for the AO55 are telemetry (or SCADA), distributed control systems, programmable controllers, data logging, and chart recording.

For replacement AO55 electronics, use the Seametrics AO55 Replacement Module. This module contains the same electronics and display found in AO55 transmitter but in a package that makes replacement simpler.


  • Two-wire 4-20 mA output
  • Can be meter or wall mounted
  • Test switch to force 4 and 20 mA outputs
  • Electronic components potted solid in urethane for maximum moisture protection
  • Rugged cast aluminum housing with fused coating
  • Variable averaging to smooth output from particularly turbulent flows
  • Exact digital setting of the 20 mA flow rate
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