Mektron, Inc. - Alpha Gear Drives - SP - Low backlash planetary gear reducer

A B/W floatless 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. Inasmuch as all BW 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 A 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 A 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 flux which - following the lines of least resistance -circulates through the shortest path. As shown in Figure 1, this is through the lower bar of the laminated core on which the secondary coil is mounted. This magnetic flux induces a voltage in the secondary or electrode circuit coil. No current can flow 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 flow 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 into 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 flow 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 BW induction relays.

RELAYS

	1500 Series Induction style conductivity liquid level or sensing circuit relay. Versatile for pump, alarm and long distance applications with field convertible contacts. Rated at 25Amps, U.L. & C.S.A. recognized.

	5200 Series Solid state conductivity or sensing circuit relay. Both fixed and adjustable sensitivity, 110\ 220 Volts, DPDT load contacts. U.L. & C.S.A. recognized.

	5300 Series Intrinsically safe conductivity or sensing circuit relay, fixed or variable sensitivity, DPDT high and low power contact rating. From 10Amps to 25Amps, FM & C.S.A. approved. For Class I, II, III, Div. 1, Groups A thru G.

	5400 Series Solid state, octal base plug in style, conductivity or sensing circuit relay. Economical, compact rugged design with LED indicator, and variable sensitivity. Literature- .pdf (130KB)

	5500\ 5510Series Intrinsically safe conductivity or sensing circuit relay, low cost with SPDT, 10Amps, load contacts. U.L. recognized for Class I, II, III Div 1 Groups A thru G.

	5600 Series Solid state conductivity or sensing circuit. Relay, open chassis design, low cost, SPDT load contacts. Available in 12, 24, 110 or 220 Volts. U.L. & C.S.A. recognized. Installation Manual- .pdf (201KB)

The diagram below illustrates a basic pump down control used on systems for storm drainage condensate return, septic tank effluent, sewage lift stations, water-soluble machine tool coolants, and cooling tower sumps.

While any of the B/W relays can be furnished, the Type 1500 induction relays are indicated. These have heavy duty load contacts that are capable of directly operating single phase pumps up to 1 H.P. @ 120 or 240 Volts A.C., or up to size 5 motor starter coils.

The Model AD2C for pump down (or AU2C for pump up) has a common power supply thru the B/W panel to energize the pump control circuits. For many applications it is desirable to have the pump motors and/or their motor starters on their own power supplies. For these situations Model AD21 for pump down or AU21 for pump up) has an isolated load contact for each pump control circuit and should be used.

B/W Alternators are compact packaged units designed to provide automatic change in the operating sequence of any number of pumps on either "pump down" or 11 pump up" level control applications. They provide unit form usage of all pumps under normal operating conditions - yet permit use of full pumping capacity during peak load periods.

Sequence changing is accomplished with a B/W designed motor operated switch that has proved its reliability on thousands of applications. This alternator provides momentary time delay to prevent false operation or rapid cycling, and it retains proper sequencing even after a power failure. In addition there are two B/W level detecting relays and all controls are wired to barrier type terminal blocks.

Enclosures are available to meet all indoor and outdoor location requirements. A complete easy to read system wiring diagram is provided showing all of the field connections so that installation is quick and easy.

Models can quickly be furnished to meet special application requirements. Extra features include: selector switches, pilot lights, and additional control functions. Also, alternators can be combined with signals and alarms as described on page 4. Systems complete with motor starters are shown on pages 8 & 9.

The standard B/W method of alternation automatically changes the sequence after each pumping operation after all pumps have stopped. Sometimes other methods of operation may be desirable and B/W offers choice. When manual sequence selection is desired, a rotary selector switch is provided and it can be located either on the cover or on the back plate inside the enclosure.

Many systems have continuous flow, and multiple pumps are used to handle the varying load conditions. For these applications B/W has a rotating sequence alternator that will change the pumps in operation whenever there is a significant change in the reservoir level. The pump that has been idle the longest will be added to those running, or the pump that has been running the longest will be stopped. Systems are available for up to 10 pumps.

In addition, B/W alternators can be built to operate fewer pumps than the maximum design number - with provisions made for easy conversion in the field to add the additional pumps when the need arises.