Rythmatic type 46 control relay circuit

Circuit: A simple series type filter is used. The feed to the bridge rectifier and the galvanometer relays is tapped off the filter coil through a capacitor. The limiter serves to restrict the voltage of the rectified signal applied to the galvanometer relays.

Moving iron galvanometer for a ripple relay

The signal coil is shown surrounding the top magnet. The movable counter balances on the bottom iron bar sets the resonant frequency. The closing contacts can be seen above the spring coil.
Note: Automatic Telephone and Electric (ATE). Previously known as ATM and later as Plessey Telecommunications Ltd. (PTL) and then as GEC-Plessey Telecommunications Ltd. (GPT).

Ripple relay with front cover removed
Receiving relay block schematic
Tuning a ripple plant series inductor

The generator frequencies used in NZ were from 175 Hz to 1050 Hz, and usually different in each network area to avoid interference. The more common frequencies are in the lower frequency range such as 283 and 317Hz. Attenuation is greater at the higher frequencies and they were gradually phased out.
(The TEPB technician depicted is Chris Johnson who later worked for the DSIR and went to the Antarctic )

Series tuned circuit layout

On the back left is the ripple frequency injection transformer connected to the generator output. On the right is the local 50Hz supply transformer.

Transistorised rhythm generator
Circa 1950's substation Rythmatic Control Cubicles

The photo on the left of the contactors on the output of the main signal generator illustrates the reason for a limited number of Rhythms used. The ealier single phase contactor depicted on the left of the picture had high inertia and the contacts prone to deterioration due to sparking. The lighter contactor illustrated on the right allowed the use of more signal rhythms.

The modern injection technology is the static frequency converter. Electronics is used to generate the injection signals which are again applied to the network via an isolation transformer and a tuned circuit. A much greater range of output frequencies and control coding is available by this method.

Circa 1980 galvanometer based ripple relays were replaced with transistorised receivers which were capable of receiving more complex signalling and varying frequencies.

ATM ryhthmatic test set - circa 1950's
A 1980's Plessey Rythmatic Control Test Set
Uniselector basis


Elements of an Uniselector: The basis of a uniselector is shown on the left. The attraction of the armature causes a pawl, which engages with a ratchet wheel, to push the switch wipers from one contact to the next. The contact banks for the wipers normally contain up to 8 levels each with 25 contacts.

The contacts on each level are equally spaced and arranged in semi-circular formation. The contacts are insulated from each other and the levels are separated by spacers.

The wipers are arranged in pairs so that both sides of the contacts are "wiped" . The pairs of wipers are mounted on, but insulated from a hollow spindle which is an extension of the ratchet wheel. Connection is made to the wipers by means of brushes of phosphor-bronze wire or twin flat-strip springs riding in collector rings at the base of the wipers.


Plessey pamplet advertising ripple control - circa 1950's

An Early Patent and Installation:
In the first years of electricity supply the greatest demand came from lighting loads.
Joseph Routin in 1897 took out British Patent 24.833 for a system for superimposing on the mains a DC or AC signal for controlling loads. This allowed the adoption of tariffs to suit the load curve of generating stations.

Duddell, Dykes and Handcock circa 1910 installed at Maidstone, to control initially street lighting and later water heating, a system that superimposed on the normal supply an AC signal of 10V at 200 Hz. The receiver was an electro-magnetic relay with a capacitor in series with the relay coil to form a tuned circuit having a low impedance at 200 Hz.

Circa 1950's street light with relay


  General Assembly: The ATM (Automatic Telephone Manufacturing Company) Type 46 Control Switch comprises two galvanometer relays, a resistor, an electrical filter, a capacitor, a bridge-type selenium rectifier with voltage limiter, and a mechanical-locking switching relay. These components arc mounted on both sides of a moulded baseplate, which also embodies the terminal block.

 Rythmatic type 46 control switch


Plessey Rhythmatic Control System
Interior of Ripple Plant Room

The earliest technology was the motor generator set. An electric motor is used to spin a generator which supplies the desired injection frequency. A contactor is used to apply the injection signal to the network via an isolation transformer and a tuned circuit.

Ripple signal parallel injection schematic
Synchronous motor driving cams for rhythmatic pulse control
old and new single phase contactors for generator output pulsing
1950's substation ripple control desk top
1980's Remote Ripple plant and load monitor unit

Uniselector based supervisory systems: The basis of a simple uniselector based supervisory system is to have two uniselectors - one in each of two stations remote from each other - and by means of interlocking circuits to cause both uniselectors to select the same outlet.

The operator on selecting a control switch "marks" a point on the sending uni- selector. In the Tauranga Electric Power Board’s system, using V.F. Pulse length telemetry, this causes a long pulse to be sent and this is detected at the receiving uniselector which pauses to allow a relay to release and enable the appropriate control function.

Starting in the 1970's the uniselector based supervisory systems were gradually replaced with microprocessor based systems. This enabled the continuous processing of analogue information and enabled faster signalling speeds, responses, and more information to be transmitted.

W.L. Kidd. "Development, design and use of ripple control" Proceedings of the IEE. Vol. 122, No. 10R, October 1975.
Content Check:
Thanks to R. A. (Roger) Jamieson.