Beckwith Electric M-2025B Current Loop Interface Module

Current‑to‑Voltage Analog Converter used with the M‑2001 Series

Digital Tapchanger Controls to provide positive tap position knowledge

• Connects easily to the M-2001 Series Digital Tapchanger Control using

an included 3 foot 6-pin connector

• Provides a 6-position terminal block for easy connections

• Enclosed components permit user to select one of four current range

configurations

• Small size permits mounting on any flat surface at least 4–5/8" wide

and 2–5/8" high

The M‑2025B Current Loop Interface Module is a current‑to‑voltage analog

converter that is used with a suitable analog position‑to‑current transducer

and the M‑2001 series of Digital Tapchanger Controls to provide positive

tap position knowledge of an LTC transformer or regulator. Components

required to configure the M‑2025B and interface with the M‑2001 are

included.

Current Loop Configuration

The configuration to use Tap Position by Positive Knowledge (Current Loop)

Procedure is shown in Figure 1 and typically includes:

• Tapchanger position output (shaft movement)

• Selsyn Transmitter

• Tap Position Monitor

• M‑2025B Current Loop Interface Module

• M‑2001 Series Digital Tapchanger Control

Tapchanger Position Output (Shaft Movement): Most LTC tapchangers have

an output shaft whose angular rotation and position are a mechanical analog

to the tapchanger tap position. In many cases, the total range of tap positions

is represented by one or two rotations of this shaft.

Selsyn Transmitter: This transmitter is mechanically connected to the

tapchanger position output shaft.

The Selsyn transmitter is an electromagnetic device used for transmitting data

on rotational position. Selsyns, or synchros, as they are sometimes called,

resemble small electric motors. They have various configurations of internal

windings. One or more windings are on a rotor and usually three windings

(stator), are stationary surrounding the rotor. By exciting the rotor windings

with an AC signal, induced voltages in the stator windings can be compared

in amplitude and polarity to determine the angular position of the rotor, relative

to the stator windings.

Tap Position Monitor: This device compares voltages from the stator windings

of the Selsyn transmitter to determine the rotor position.

The position information is converted to a tap position number and is usually

displayed on the front of the unit. This device includes an analog current output

that corresponds to the displayed tap position.

Beckwith Electric M‑2025B Current Loop Interface Module: This device accepts

the current loop output and properly scales it by the use of an external resistor.

It also is configured by a jumper to select a unipolar or a bipolar current loop

input. It provides an analog voltage output to the M‑2001 Series Control that

tracks the analog current output of the Tap Position Monitor.

The lowest analog dc voltage corresponds to the lowest tap position number

and the highest dc voltage corresponds to the highest tap position number.