General Electric Company Solid-State Logic part3

11 ·4 GENERAL ELECTRIC POWER SUPPLIES

The logic system operates on d-e voltages, and the 115 volts a-c must be converted to those appropriate voltage levels.

The logic-element power supply (LEPS) (Fig. 11·38) converts filtered 115 volts a-c to 12 volts and 125 volts d-e. Zero volts, P+, and -12 volts, P-, are the basic power buses utilized to operate the logic elements, built-in monitor lights, and out put-amplifier triggering circuits. The current capacity of each supply is 5 amp at 12 volts d-e.

The zero-volt bus, referred to as logic common, is also com mon with respect to the -125-volt d-e bus which powers the original input. It has a maximum current rating of 200 rna, which is equivalent to 40 simultaneously conducting original inputs.

The -+- 12-volt a-c source LD is an auxiliary connection required by the sine-to-squ are wave converter.

The capacity of the power supply to drive elements varies with the type of unit and depends on whether monitor lights are used. However, a good approximation can be made by con sidering the 12-volt capacity equal to a total of 600 load units . Each logic function is counted as one unit of load except those listed in Table 11 ·1.

A diversity factor may apply to the relay output amplifier and internal monitor lights as the individual circuit is considered. If more than one power supply is required, the -125-, -12-, and 0-volt buses should be wired in parallel with additional power supplies.

The zero-volt bus, logic common, is to be connected to a good water-pipe earth ground. The 12-volt nominal voltage should not be permitted to go lower than 10.5 volts or above 15 volts. A logic power supply is illustrated in Fig. 11·39.

The incoming 115 volts a-c must be filtered as shown in Fig. 11 ·40. The choke-capacitance filter is very effective in the 115- volt a-c circuit, and if one side of the line is grounded near the LEPS, only one set is required. A one choke and one capaci- · tor combination is shown in Fig. 11·41 and is available under one number, CR245X103A. One filter set can accommodate up to four power supplies. A l-amp power supply ( 120 load units) and a 10-amp power supply ( 1,200 load units) are also available.

When the logic system is operated by batteries, limit switch, push-button, or other pilot-device information is also required by the control. It appears simpler to statically convert 12 volts d-e to 125 volts d-e than to utilize a second bank of

batteries. The converter, shown in Fig. 11 ·42, Is a panel-mounted device requiring an input of 9 amp at 12 volts d-e, with a resulting output of 0.8 amp at 125 volts d-e. It can supply up to 160 conducting inputs.

When 24-volt d-e output amplifiers are employed in a static system, a source of 24-volt power must be available. This power supply will normally have 115 volts a-c as an input and the rated 24 volts d-e nominal output. The current required will

be determined by the maximum number of loads conducting at one time plus a margin for future loading.

The maximum open-circuit voltage that should be applied to the amplifiers is 28 volts. The power supply must be filtered . When higher voltage is applied, too much current will be drawn by the load, and an overvoltage will also be applied to the unit. The minimum voltage applied depends upon the load, but a good guide can be 22 volts. Each amplifier will have up to a 1-volt drop within the device, which will result in somewhat lower voltage applied to the load.

The primary characteristics to consider in choosing the power supply are ( 1) regulation of the 24 volts with loading com bined with incoming a-cline variations, and (2) maximum open circuit voltages as read by a 20,000-ohms-per-volt voltmeter.

When the solid-state proximity switch is connected directly into static control, a special power supply must be utilized. Five proximity switches can simultaneously be connected to a single power supply as shown in Fig. 11 ·43.

Terminals L 1 and L2 will have 115 volts a-c connected in addition to a terminal for logic common, zero volts from the LEPS, and terminals for the four wires from the switch. The black, green, red, and white wires of the proximity switch will be connected to the power supply, the white wire being the logic level signal to be connected to the proximity-switch input. The white and red wires from every switch must be individually insu lated shielded cables, with each shield connected only to one point, LC, at the power supply. All four limit-switch wires must also run in steel conduit back to the power supply if they are exposed to power wires. The black, green, and red wires each have three terminal points on the power supply; therefore no more than two wires need be terminated under one termi nal point.

11 ·5 SPECIAL FUNCTIONS

Any logic control circuit can be built using the five basic logic functions: AND, OR, NOT, MEMORY, and DELAY. But when certain combinations of logic functions are repeated many times in a logic circuit, a special unit can be devised to perform the func tion as well or better, in some cases, with a reduction in required panel space and at a lower cost.

The step MEMORY is a special unit and is most useful in count ing circuits and information-handling applications. The step MEMORY (Fig. 11·44) is a modification of the off-return MEMORY, with a unique turn-on and turn-off input network.

Pin 5 and pin 6 are steer inputs which direct pin 2 in the proper part of the flip-flop when an input signal is applied to the step terminal. The best analogy is that the steering network is like a double-barreled shotgun, with pin 5 and pin 6 being the hammer for each barrel and pin 2 the trigger. The only moment the gun will fire a shot down a barrel is when a particu lar hammer is actuated and the trigger is pulled . The time rela tionship in this analogy is accurate in that the particular hammer that is actuated may change up to the moment the trigger is pulled and may again be changed after the trigger is pulled . One pull of the trigger will cause only one shot, and the trigger must be released and pulled again to cause another shot. The firing of the shot occurs when the trigger is pulled, not while being held nor upon release of the trigger. The firing of the shot down a particular barrel will cause pin 8 to turn on and pin 7 to turn off, or pin 7 to turn on and pin 8 to turn off, depending upon which barrel is fired.

With an ON signal at pin 5, steer on, and a step signal applied at pin 2, the internal flip-flop will assume the state in which the standard output, pin 8, is ON. Likewise, with an ON signal at pin 6, steer off, the result would be pin 7 in the ON condition. It is obvious that there should never be an ON signal applied to both pin 5 and pin 6, since the unit would then be arranged to do two opposite things at the same time , which would not be a logical application of the step MEMORY.

Pin 3, unit reset, must be connected to the unit-reset module, as previous units required such a connection to their pin 5. Pin 1, set, provides a method to turn on pin 8 by loss of an ON signal to its terminal. This is commonly called setting a flip flop. Pin 4, reset, can reset the flip-flop by loss of an ON signal to its terminal. The reset state of the step MEMORY is when pin 8 is OFF and pin 7 is ON. The set and reset terminals override the steering network in their effect. For example, if pin 1 does not have an ON signal, pin 8 is ON; if pin 2 is stepped, no change in the output of the step MEMORY occurs. These terminals pro vide a method for changing the output condition independent of the steering network; this method is very useful in resetting a counting circuit to zero or placing a predetermined number in a counter circuit and then continuing the counting from that number.

It can be seen in Fig. 11·45 that set and reset override the steering network, and the network is capacitively coupled with the flip-flop. With an ON signal, 0 volts, applied to one steer terminal, there will logically be an OFF signal, -4 volts, at the other; when an ON signal is applied to pin 2, only one capacitor will charge up, causing the appropriate AND-NOT in the flip-flop to commence conducting. This momentary conduction turns the other AND-NOT off, which results in flipping the flip-flop in the new maintained condition. The ON signal to pin 2 must be re moved, and then -4 volts applied at the terminal in order to have the steering network properly reorient itself for application

of another step pulse. The recommended maximum pulse rate which can be received by the step input, pin 2, is 10 kilocycles per second.

The step MEMORY is available in the off-return or retentive form, with operating speeds and terminal connections the same in both cases. The difference is only what state the flip-flop will assume on regaining system power ( 12-volt d-e previously hav ing been removed). The OFF state, in which pin 8 is off and pin 7 is on, is given by the step (off-return) MEMORY type. The state existing prior to power interruption is given by the step (retentive) MEMORY type. The outputs of the step (off-re-turn ) MEMORY can each drive up to 12 other inputs. The outputs of the step (retentive) MEMORY can drive up to seven inputs.

The bi-step MEMORY is shown in Fig. 11·46. This off-return type of unit is similar to the step MEMORY, except that it has two complete steering networks in place of one. It is useful in add-subtract counters and reversible shift registers, each of which is norma1ly limited to a unidirectional advance.

The terminal for steer off for each steering network has been eliminated in the bi-step MEMORY. This function still is required by the element, but a built-in NOT of steer on is included inside each unit, thereby automatically providing a steer-off signal in the absence of an oN signal applied to the steer-on terminal.

The bi-step MEMORY has two completely independent steering networks which control a single flip-flop, and one step signal should be applied at one time. Pin 1, set, overrides each steering network by loss of an ON signal, and this results in having pin 8, the standard output, in the ON condition. The unit reset of pin 4 must be connected to the UNIT RESET, and if the reset function of the flip-flop is also required, an external AND-NOT can be used to control this input from two external signals. The bi-step MEMORY is available only in the off-return form, and each output can drive up to 12 subsequent inputs.

Most contact-making devices have contact bounce as they make a circuit, and it is necessary to remove this bounce when driving counter circuits and information storage registers. The signal amplifier incorporates an antibounce circuit, in addition to being able to simultaneously drive 50 logic functions, com pared with the normal 12-unit loading capability.

Upon receiving an ON signal from a pilot device via an origi nal input, an output will lock ON for 10 to 15 milliseconds ( msec) regardless of whether the input signal bounces on-off or stays off. If an input signal is still there after 15 msec, an output from the signal amplifier will continue until the input is removed. If the input is removed prior to the 15 msec lock-ON time and remains OFF, the unit will turn OFF after 15 msec.

A dual function is also incorporated in the signal amplifier to take one logic input and provide an output capable of supply ing up to 50 input signals into subsequent logic functions.

The single-shot unit is very useful in circuit designs incorpo rating MEMORYs, since they exhibit a first come, first served input configuration. A maintained signal can be made into a momen tary signal by interposing the single shot. It provides an output of approximately 100 -tsec for a maintained input. An input must be removed and again applied to yield another 100-,usec output signal.

An adjustable-single-shot unit is also available (Fig. 11·47). This function produces a standard output for a set period of time with a momentary or maintained input signal. It is adjust able from 0.006 to 0.3 sec and can be extended to 12 sec by ·

connecting an external capacitor to socket terminals 3 and 4. A typical application of this unit would be the energizing of a solenoid valve for a short set period of time regardless of the length of the input signal. This module takes the place of the whole circuit shown in Fig. 11 ·48.

The unit-reset auxiliary unit is required for all MEMORYs, DELAYS, sealed AND logic functions, and step MEMORYs to make their output condition dependent upon application of system power. This individual unit can simultaneously be connected to 50 inputs, and supplies a delayed ON signal to these units.

As system power is applied to the logic panel, the output of this unit is in the OFF condition for approximately 15 msec, and then the unit provides an ON signal continuously at its out put, terminal 8. It only provides this delayed ON signal upon application of system power and then is always in the ON state. The unit reset must be used with logic functions containing flip flop circuits and has a 50-unit driving capability.

The probe test light shown in Fig. 11·49 is the basic test unit for a static control panel which is plugged into a spare socket. Two monitor lights are incorporated within the module, one indicating whether an ON signal or an OFF signal exists at the black test lead.

The black test lead will be used while power is present on the panel and can be employed while the static system is operat ing without disturbing the operation of the panel.

The red lead is to be used with the terminal marked SIGNAL and is a continuous ON signal to simplify manual insertion of an ON signal into the logic system. It is equivalent to manually

operating a relay in a conventional panel and therefore is color coded as red to signify caution in its use. A logic unit can be tested in place by the use of the red lead as an input and the black lead as an output monitor. Each logic input and output signal is accessible in the panel, and the probe test light is a direct , simple, and convenient method to test each unit or the system function. It must be used only on logic-level signals, not on 125 volts d-e, 24 volts d-e, or 115 volts a-c.

By the addition of a temporary jumper wire between terminal and terminal 2, the test lead will act as a memory if an ON signal becomes present and then turns OFF. This is very useful in checking limit-switch continuity into a panel. The test lead is on the logic side of the input, and then the switch is actuated. The probe light will operate its ON light if an ON signal appears at the test lead and will remain ON. Thus, to check an external switch, the probe test light will monitor the panel while the switch is actuated and then display the results until manually reset. By disconnecting the jumper or touching the jumper with the red signal lead, one can reset the memory circuit with the ON monitor light.

11 ·6 ACCESSORY DEVICES

Most logic functions are packaged in a plug-in module. This element is protected by a removable nylon cover, designed to give maximum protection from vibration, shock, and corrosion.

This well-protected and easy to handle element plugs into a base assembly (Fig. 11·50). Each module can be plugged into its socket in only one orientation to assure proper connections and has color-coded nameplates on the top of each cover. The nameplate shows the logic-symbol terminal connection numbers and catalog number.

Sockets for the modules are available on assembled base rails in 5-, 8-, 11-, and 17-unit lengths. Wiring connections to each base are made to screw-type terminals, similar to a terminal

board, and each screw-terminal number is identified in the phenolic molding. Power connections to each socket are made by heavy bus bars as shown in Fig. 11·51, and power termina tions are made to the bus bar by sectional terminal blocks.

Top, bottom, and middle retaining covers with associated clips are available to provide an enclosed wiring trough. One set of top and bottom covers would be used in addition to the appro priate number of middle covers to form a neat appearance in a panel (Fig. 11·52).

The mounting-track method of mounting the single 125-volt d-e original input elements allows a few screws to mount 3 ft of track and 34 input points. The elements snap into the track and are retained by two edges on the track that grip the two slots on the element. Spacing is maintained by the bus bar de scribed in the foiiowing section.

The standard 3-ft length is slotted to permit easy instaiiation and removal of each element and can be quickly cut to shorter lengths by a hacksaw as desired.

Each zero-volt connection to the 125-volt d-e original input must be made by the recommended bus bar. It has seven holes which can accommodate six inputs plus the connection to a subsequent bus bar. A bus bar is recommended for convenience of wiring and as the simplest way to maintain spacing between inputs and minimize voltage drop in the zero-volt reference.

Summary

The General Electric Company system of solid-state-logic “static control” covered in this chapter is an English logic system providing basic building blocks of AND, OR, NOT , MEMORY, and DELAY. There are several special units available for use in count ers and shift registers.

The basic transistor switch is the heart of aU logic elements in this system. The patented circuit of the General Electric Com pany transistor switch is a self-biasing circuit requiring only a single 12-volt supply for operation of the logic element. The General Electric Company system uses a 0-volt d-e signa l as · an ON signal and a -4-volt d-e signal as an OF F signal.

This system uses the English logic NEMA symbols, with the NOT outputs of MEMORY elements shown by a smaii NOT symbol as part of the overall basic function symbol. This form of com bination symbol indicates that the element has the inverted, or NOT, output available at one of its plug-in pins . This usually reduces the available number of inputs. The basic AND has three inputs, but the AND with NOT output available has only two inputs. This is necessary because the system uses a standard 10-pin plug-in module for packaging.

This system utilizes a plug-in component for all logic elements, and rather conventional wiring techniques are all that are required for field connections. The basic AND, OR, and NOT functions are packaged two in each plug-in unit. Should a com ponent fail in one of these units, all that is required is to replace it by plugging in a new unit without disturbing any wiring. A plug-in test unit is also available and should be included in each panel, as it provides the best possible test equipment for use on this system.

Electrical noise on input signals must be guarded against as in all static systems. General precaution indicates that all input wires should be run together in their own steel conduit and all output wires should be run together in their own steel conduit; logic wires should never be taken out of the control panel; sensor wires (photocells, etc.) should be run with twisted shielded pair; and inductive loads (driven by contact-making devices) mounted near the logic should be suppressed. General Electric Company now has a system with higher noise immunity available called Series A. Series A logic elements are so designed that the requirement for running input and output wires in separate steel conduits may be eliminated.

The recommended voltage for use with contact-sensing devices is 125 volts d-e or 125 volts a-c. Power amplifiers are available for static output up to 10 amp at 115 volts a-c.