ELECTRICAL AND ELECTRONIC CIRCUIT ANALYSIS
There are many electrical and electronic circuits used in ordnance equipment. These circuits perform such jobs as power supply, lighting, loading system control, train and elevation control, and overload protection. All electrical circuits are made up of basic electrical or electronic devices. These devices, individual y or working together, can delay, interrupt, isolate, or integrate electrical and electronic circuits, and prevent damage to equipment.
The purpose of this chapter is to provide functional information of how these devices are used to operate and control ordnance equipment. Portions of this chapter are based on foundational information contained in other training manuals. You are assumed to have a knowledge of the fundamental properties of electricity and how to operate a multimeter to read voltage, resistance, and amperes.
Before proceeding with this chapter, you should review the information in Navy Electricity and Electronics Training Series (NEETS), Modules 1,2,3, and 16, Introduction to Matter Energy, and Direct Current, NAVEDTRA 172-01-00-79; Introduction to Alternating Current and Transformers, NAVEDTRA
172-02-00-85; Introduction to Circuit Protection, control, and measurement, NAVEDTRA 172-03-00-85; and Introduction to Test Equipment, NAVEDTRA 172-16-00-84, respectivey.
First we will explain some of the more common electrical and electronic devices used in missile launcher and gun mount control circuits. Next we will describe the operation of the common types of control circuits and explain the procedures used to locate common failures within each circuit. We will then discuss the control system in the Mk 45, Mk 75 gun mounts and the Mk 13 Mod 4 GMLS. These control systems are similar to the Mk 26 GMLS, so the Mk 26 GMLS will not be discussed.
The final sections of this chapter are devoted to a discussion of ships power and distribution and the fundamentals of synchros and electrical safety. Safety precautions required for working with electrical and electronic equipment are provided throughout the chapter.
POWER SUPPLY AND CONTROL CIRCUIT COMPONENTS
LEARNING OBJECTIVE: Recall the electrical components used in a typical missile launcher/gun mount power supply and light-ing circuit, their function, and how they are tested.
All the mechanical, electrical, and hydraulic mechanisms in a modern gun mount/launcher are controlled by the action and interaction of the various devices of the control and power circuits. The control circuits regulate the application of power to motors and to solenoid-operated hydraulic valves. Operation of the gun mount/launcher is performed sequentially. Barring a malfunction, no action (hydraulic, mechanical, or electric) can occur out of sequence because of the interlocking action of switches, relays, and solid-state devices.
Power circuits are normally 440 VAC and are used to operate the electric motors that power the hydraulic pumps associated with the gun mount. Gun mount/launcher control circuit voltage can be ac and/or dc of any value up to approximately 30 VDC or 115 VAC. Control circuit voltage is normally supplied by gun mount/launcher transformers that step-down 440 volts ac.
This portion of the chapter covers the more common electrical devices used in power and control circuits.
Indicator lights show the position of mount/ launcher components or the status of switches, solenoids, fuses, and control and power circuits.
Figure 5-1 shows a simplified circuit with a light (LI) that indicates when the motor is running. The letters L or LI are the reference designations for lights on the schematics for the older gun mounts; the new ordnance equipment uses the designation DS.
The fuse is the simplest form of a circuit protective device. It consists of a metal alloy fusible element that melts at a predetermined value of current. Thus, if a circuit draws more current than the rated value of the fuse, the fuse opens (blows) and the circuit components are protected.
Fuses are rated according to the amount of current they can safely carry; this current is usually measured in amperes. The most common cause of fuse failure is an overloaded circuit. There are, however, other causes. Failure to set the fuse into its contacts properly can cause a fuse to open.
On schematics for older gun mounts and missile launchers, fuses are designated by the letters F or FA (fig. 5-1). On newer mounts and missile launchers, such as the 76-mm 62-caliber Mk 75 gun mount and the Mk 13 Mod 4 GMLS, fuses are designated FE on schematics.
A switch is a device used for making, breaking, or changing the connections in an electric circuit. Switches are used extensively in gun mount/launcher control circuits to start and stop motors, to turn indicating lights on and off, to channel information from one point in the system to another, and to shift system mode of operation, to name but a few of their many uses.
An essential function of any switch is to maintain a good, low-resistance contact when the switch is closed. A poor connection between switch elements produces considerable resistance. This resistance results in overheating the contact area. When heavy current is being carried by the switch and the switch contacts are opened, an arc is produced. Therefore, switches should be opened and closed quickly to minimize arcing. Usually, they are designed to have snap action.
Switches are classified by the number of poles, by the throw, or by the number of positions. The pole of a switch is its movable blade or contactor. A switch may have one or several poles. The throw of a switch indicates the number of circuits each pole can complete through the switch. The number of positions a switch has is the number of places at which the operating device (toggle, shaft, plunger, and soon) will come to rest and, at the same time, open or close a circuit. As shown in figure 5-2, switches through which only one circuit can be completed are called single-pole, single throw switches. Switches with two poles, through each of which one circuit can be completed, are described as double-pole, single-throw switches, whilethose with two poles, through each of which two circuits can be completed, are described as double-pole, double-throw switches.
Switches are also classified by method of actuation (push button, toggle, and rotary) and by the trade name
Figure 5-2.-Switch classification according to number of poles and throws.
Figure 5-1.-Power-on indication circuit.
of the manufacturer. An example of this type of classification is the microswitch.