AMETEK 1500 Induction Style Relay User Manual

1500 series, Nstallation, Ervice

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1500 Induction Control Relays

1500 Series

NSTALLATION

& S

ERVICE

ANUAL

Principle of Operation

A B/W fl oatless liquid level control system consists of a relay

of the proper type, a holder designed to support one or more

electrodes or probes in the liquid container, and the corrosion

resistant electrodes themselves. In as much as all B/W induction

relays are quite similar differing only in contact arrangement, the

following description of how a 1500-C Relay functions on a

pump down control application will serve to explain the design,

construction, and operating principles for the entire line.

As shown in diagrams below, the laminated core of the relay is

shaped. The primary coil is assembled to the upper bar of the

core, and the secondary coil for the electrode is placed on the

lower bar. An armature located below the legs of the core is

connected to an insulated arm carrying the movable contacts.

When the armature is raised, these contacts close or open

the motor and electrode circuits, depending upon whether the

contacts are normally open or closed. (Contacts shown normally

open in this example).

When a source of alternating current is connected to the primary

coil at terminals 3 and 4, the primary coil sets up a magnetic

fl ux which circulates through the shortest path following the lines

of least resistance. As shown in Figure 1, this is through the

lower bar of the laminated core on which the secondary coil is

mounted. This magnetic fl ux induces a voltage in the secondary

or electrode circuit coil. No current can fl ow in this coil, however,

until the circuit is completed between the electrodes. Thus, the

electrode circuit voltage being generated within the relay has no

connection with the power line.

The B/W 1500 induction relay utilizes the liquid as an electrical

conductor to complete the secondary circuit between the upper

and lower electrodes. Thus, when the liquid contacts the upper

electrode, the resulting fl ow of current in this circuit sets up a

bucking action in the lower bar of the core. This action tends

to divert lines of magnetic force to the core legs and sets up an

attraction that pulls the armature in to contact with the legs, as

shown in Figure 2. This armature movement closes the electrode

and load contacts.

The lower contacts on 1500-C Relays (terminals 9 and 10)

connect the secondary circuit to ground when liquid contacts

the upper electrode and act as a holding circuit to maintain the

relay in its closed position until the liquid falls below the lower

electrode. This holding circuit provides control of the relay over

any desired range in the liquid level, depending on the distance

between the upper and lower electrodes.

The fl ow of current through the low energy secondary circuit

is very small and varies with the voltage of the secondary coil.

The secondary coil is selected to operate over the resistance

of the liquid being controlled. Accordingly, since there is a wide

range of secondary coils from which to choose, it is important

that complete information regarding the nature of the liquid be

furnished when ordering B/W induction relays.

FLUX

ARMATURE

FLUX

ARMATURE

PUMP START
ELECTRODE

PUMP STOP
ELECTRODE

A.C. LINE

TO MOTOR STARTER

A GOOD DEPENDABLE
GROUND RETURN
CONNECTION TO THE
LIQUID IS REQUIRED

GROUND:

Figure 1 - Secondary coil circuit open; armature down.

Figure 2 - Secondary coil circuit closed; armature up.