Chapter 1 - 360 Telescope Electronics


1.1 Introduction

The 360 Electronics are mostly compatible with the VLT standard, and it consists of several subsystem. Each subsystem has been built around a local computer (VME).The descriptive chapters are organized in the same way, by subsystem. However, several electronics units have no direct relation to VME computer and cannot be classified under a VME system. This chapter gives descriptions of the 360 electronics in general and of electronic system which are not directly related to specific VME computer.

1.1.1 Reference Information

The following sections give specific information:

Section 1.2 gives a general description how the abbreviation of all the computer I/O signals in the 360 are organized.
Section 1.3 describes the VME power supplies. Also provides information related to P2 connector Analog and Digital signal assignments.
Section 1.4 provides a list of drawings and data sheets, and other maintenance information.

1.2 360 Telescope Signals

This section introduces naming conventions for the 360 signals connected to a VME computer. For each signal, an abbreviation is defined that is used in the hardware drawings and software.

1.2.1 Abbreviations

The abbreviations are defined as follows:

Two characters to define the VME computer, which is the same as the Ethernet node. For example AL for alpha.
Two characters generally to define the main subgroup. For example PA for power amplifier.
The rest of the abbreviation (up to a maximum of 10 characters) to define the signal.

The following VME systems have been defined:

AA: Cassegrain Adapter
AD: Instrument ADONIS
AL: Alpha
DE: Delta
DO: Dome
CA: Console A
CB: Console B
CC: Technical CCD
EF: Instrument EFOSC
HA: Instrument HARPS
HB: Hydrostatic bearing
IL: Interlock System
M1: Mirror 1 Lateral Pads
M2: Secundary Mirror
RO: Cassegrain Rotator

The signals of each VME system are described in separate chapters. However, some VME systems are combined in one chapter: AL & DE. This is done because the systems are identical. This structure provides easy access and maintenance. Another field in the description defines the type of the signal:

DI*n: Digital input; n bits
DO*n: Digital output; n bits
AI*n: Analogue input; n significant bits
AO*n: Analogue output; n significant bits

1.2.2 Level Convention

The defined level of the digital signals refers to the level at the digital I/0 board connection. There are however; "high true" and "low true" signals: "low true" signals are indicated with an asterisk(*) in the abbreviation.

The definition "asserted" (= "true") and "negated" (="false") always refers to the description of the signal: it is not concerned with voltage level.


The VME boards which are used in the 360 Telescope local computers are commercial boards. For detailed technical information on each VME board, please refer to the corresponding manual.

1.3.1 Power Supplies

There are two possible power supplies, depending on the power required by the VME system:

ELBA power supplies. In this case there are 2 power supplies: 5V/40A (type ESP81540) and + and -12V/4A (type ESP82153).
LK power supply LKP3151. In this case there is 1 power supply which provides the three voltages. This supply has no sense lines and therefore, the 5V must be adjusted. This can be done by modification of R29 inside the power supply. A correct voltage on the VME backplane is achieved with R29=14k7. Because this modification is necessary, the LK supplies should not be used for new designs.

1.3.2 P2 Connector Analog signal assignments




1a CH00 1a CH16 1c CH00HI 1c CH00LO
3a CH01 3a CH17 3c CHO1HI 3c CH01LO
5a CH02 5a CH18 5c CH02HI 5c CH02LO
7a CH03 7a CH19 7c CH03HI 7c CH03LO
9a CH04 9a CH20 9c CH04HI 9c CH04LO
11a CH05 11a CH21 11c CH05HI 11c CH05LO
13a CH06 13a CH22 13c CH06HI 13c CH06LO
15a CH07 15a CH23 15c CH07HI 15c CH07LO
17a CH08 17a CH24 17c CH08HI 17c CH08LO
19a CH09 19a CH25 19c CH09HI 19c CH09LO
21a CH10 21a CH26 21c CH10HI 21c CH10LO
23a CH11 23a CH27 23c CH11HI 23c CH11LO
25a CH12 25a CH28 25c CH12HI 25c CH12LO
27a CH13 27a CH29 27c CH13HI 27c CH13LO
29a CH14 29a CH30 29c CH14HI 29c CH14LO



1.3.3 P2 Connector Digital signal assignments


PORT 0 I/O Bit 0 B32
I/O Bit 1 B31
I/O Bit 2 B30
I/O Bit 3 B29
I/O Bit 4 B28
I/O Bit 5 B27
I/O Bit 6 B26
I/O Bit 7 B25
PORT 1 I/O Bit 8 B24
I/O Bit 9 B23
I/O Bit 10 B22
I/O Bit 11 B21
I/O Bit 12 B20
I/O Bit 13 B19
I/O Bit 14 B18
I/O Bit 15 B17
PORT 2 I/O Bit 16 A32
I/O Bit 17 A31
I/O Bit 18 A30
I/O Bit 19 A29
I/O Bit 20 A28
I/O Bit 21 A27
I/O Bit 22 A26
I/O Bit 23 A25
PORT 3 I/O Bit 24 A24
I/O Bit 25 A23
I/O Bit 26 A22
I/O Bit 27 A21
I/O Bit 28 A20
I/O Bit 29 A19
I/O Bit 30 A18
I/O Bit 31 A17
PORT 4 I/O Bit 32 C32
I/O Bit 33 C31
I/O Bit 34 C30
I/O Bit 35 C29
I/O Bit 36 C28
I/O Bit 37 C27
I/O Bit 38 C26
I/O Bit 39 C25
PORT 5 I/O Bit 40 C24
I/O Bit 41 C23
I/O Bit 42 C22
I/O Bit 43 C21
I/O Bit 44 C20
I/O Bit 45 C19
I/O Bit 46 C18
I/O Bit 47 C17
PORT 6 I/O Bit 48 A1
I/O Bit 49 A2
I/O Bit 50 A3
I/O Bit 51 A4
I/O Bit 52 A5
I/O Bit 53 A6
I/O Bit 54 A7
I/O Bit 55 A8
PORT 7 I/O Bit 56 A9
I/O Bit 57 A10
I/O Bit 58 A11
I/O Bit 59 A12
I/O Bit 60 A13
I/O Bit 61 A14
I/O Bit 62 A15
I/O Bit 63 A16
GND B13,B14
GND B15,B16
REF Ports 0 & 1 B12
Pull-up Ports 0 & 1 B11
Protect Ports 0 & 1 B10
+5 V B1
REF Ports 2 & 3 B4
Pull-up Ports 2 & 3 B3
Protect Ports 2 & 3 B2
GND C15,C16
GND C13,C14
REF Ports 4 & 5 C12
Pull-up Ports 4 & 5 C11
Protect Ports 4 & 5 C10
+5 V B1
REF Ports 6 & 7 C1
Pull-up Ports 6 & 7 C5,C6
Protect Ports 6 & 7 C7,C8



This section contains the index of maintenance information for the 360 Telescope electronic units which are not related to any VME system. Some units are described separately, together with the drawings and maintenance information.

1.4.1 Interlocks

The operation of all motors on the telescope is governed by interlock system which prevent any dangerous manoeuvres from taking place. Interlocks are necessary to protect the telescope from damage and to ensure the safety of the operating personnel. These interlock system are incorporated in both the hardware and software of the telescope. The software interlocks are written into the computer programme to duplicate the function of the hardware interlocks. This gives a double level of protection as faulty operation of either system is prevented by the alternative sysytem.

Numerous limit switches and sensor are attached to various parts of the telescope and its mechanisms. Signals from these devices are combined logically to generate the various interlocks combinations, or logical functions, which are necessary for the safe control of the telescope. A large number of motors are used on the telescope to operate numerous locking devices, motional drives and various accessories. The operation of most of these motors is governed by different logical combinations of the interlocks signals. This prevents the motor from operating unless it is safe to do so.

A detailed description of the interlock system will be give at Chapter 5.

In order to prevent electromagnetic interference from one subsystem to the other, all these signals are coupled via relays.

1.5 Motor Control System

1.5.1 Introduction

A large number of the operating mechanisms fitted to the telescope are motorized using ON/OFF 3 phase motors. These motors are controlled by standard Motor Control Boxes (MCB's). All motors of this type are concerned with the control and manipulation of different parts of the telescope systems. Operation of the motors is an interily ON/OFF switching action controlled by relays within the MCB units. Motors

All the motors described here are three phase 380 volts satr connected. Their power consumption varies between 0.05 KW and 0.45 KW, except in the case of the platform drive system where two 0.9 KW types are used, and the main mirror hoist where a 3.0 KW is used. The motor are controlled in both directions by relay-switched reversal of the connections to two of the motor phases. Limit switches are incorporated to prevent over travel of the operating machanism in either direction. Some motors incorporates brakes so that inmediately the motor is de-energized the brake is applied. This prevents over-run of the mechanism due to is own inertia and result in more precise determination of the stopping points. After stopping the brake remains firmly applied to prevent any further movement due to gravitational forces.

Two speed braked operation of a mechanism is sometimes required to achieve a fast slewing rate combined with a slow, braked approach to the final stopping point. In this case two motors, fast and slow speed, are arranged as an in-line, coupled pair separated by a clutch. In the slow speed mode the slow motor drives the mechanism through both the clutch and the fast motor. In the fast speed mode the clutch is disengaged and the fast motor drives the mechanism independantly. General Arrangement of the Control System.

Each motor is wired directly to a junction box situated close to the motor. From there standard plug/socket fittings and cabling connect each junction box back to a motor control box. These are situated locally at convenient points throughout the telescope. Each MCB acts as a central grouping point to receive command signals and generate control signals for up to seven motors. Command signals are received from the computer, from manual pushbuttons situated locally and from manual pushbuttons in the control room.

Most of the telescope mechanisms described in this sec- -tion operate as two position devices. Where intermediate positions must be known, absolute digital encoders are fitted to the mechanisms. These encoders use hall-effect techniques and coded rotating discs to generate digital information specifying the mechanism's position. This information is transmitted directly back to the computer for processing.

A comprehensive system of hardware interlocks prevents any dangerous operations, or combination of operations, which could otherwise damage the telescope. This interlock system is realized in hardware using numerous limit switch sensors and interconnections throughout the different motor control boxes and the control room wiring. A functional description of the interlock systems is given in Section 4. Motor Control Boxes

Although there are minor variations in some of the Motor Control Boxes (MCB's) all of them are based on a standard motor control circuit and constructional layout. Each standard MCB contains all the motor control relays, interlock protection circuits, computer command interfaces and manual control facilities for the control of up to 7 motors. Each motor may be controlled bi-directionally within the extremes of the mechanism' s travel, as defined by two limit switches. In addition to its normal mode of operation via the computer (ON-LINE), the MCB has several other modes of manual operation (OFF-LINE), either locally or remotely generated. These allow emergency action to be taken on the spot, routine operational maintenance and remote manual control from the control room in the event of computer failure.

Built in indicator lights allow visual monitoring of the control status of each motor. Diagnostic indicators provide synoptic information from the general interlock system. A diagrammatic panel illustrates the logical pre-conditions which govern the operation of each motor within a particular MCB. All these facilities are designed to aid rapid fault-finding in the event of a malfunction.

1.5.2 General Motor Connection Arragements Limit Switches

Each mechanism that is. controlled by an MCB switched motor has two limit switches associated with it. These limit switches are arranged to trip at the extremes of the mechanism's travel. They act locally in the motor control box (MCB) to cut power to the motor. Once the mechanism has reached the end of its travel and the limit switch has been activated the motor can only be re-energized in the reverse direction.

All limit switches are of the normally closed type, opening when a limit is reached. They act by de-energizing a dedicated relay in the MCB unit. This method of connection results in "fail to safe" operation as a break in the wire, or failure of the relay, prevents the motor from being energized in the corresponding direction.

Linear action motors are supplied with two internal contacts to limit their range of travel. When the complete linear travel of the motor is not used, external limit switches are mounted in the normal way at the extremes of the mechanism's travel. They are then wired in series with the internal limit contacts. Motor with Brakes

Some motors incorporate brakes so that immediately the motor is de-energized the brake is applied. This prevents overrun of the mechanism due to its own inertia and results in a more precise determination of the stopping points. After stopping the brake remains firmly applied to prevent any further movement due to gravitational forces.

No special control circuit is required to activate the brake, which is normally applied when no power is connected to its single phase energizing winding. As soon as this winding is energized the brake lifts and allows the motor to run. The brake winding is wired directly across two of the motor phases so that when power is applied to the motor the brake is automatically lifted. Standard Junction Boxes and Motor Connections

All motors, together with connections from their two limit switches Fl, F2 are wired to a local junction box close to the motor. There are two sizes of standard junction box ; a small size box for connecting to a single motor, see Fig. 3.3.3-A, and a larger size for connection to two motors, see Fig. 3.3.3-B. There arc also special types of junction box for a pair of motors connected for two speed drive, see Section, and for linear action motors, see Section Although general terminal connections are described for the various types of junction box, exact details of junction box connections will be found in the old folder of paper drawings, titled DWGS VII.

Standard junction boxes act only as wiring connection points for their respective motor and limit switch cables. There are three cables from the junction box for each motor. Each cable has a separate gland connection ; one for the motor and one for each limit switch Fl, F2. The colour codes for the different motor phase connections, and all numbered terminal block connections are shown in the appropriate drawings Fig. 3.3.3-A for the small junction box and Fig. 3.3.3-B for the large junction box. In the case of the latter there is a separate terminal block for each of the two motors.

For each motor there is a separate 16 pole Hirschmann socket on the junction box. These connectors also incorporate two earth connections giving a total of 18 poles. The numbering of each individual connection to the Hirschmann connectors is identical with the numbering of the terminal blocks shown in the drawings. Type H3 cable fitted with Hirschmann plugs at each end. is used to connect the junction boxes back to their appropriate motor control boxes. This special cable consists of a screened centre section carrying 5 x 1 mm2 conductors for the three phase power lines (380V) , and an outer section consisting of 11 x 0,4 mm2 conductors for the 24 volt connections (limit switches). Two Speed Drive Using a Pair of Motors

Two speed, braked operation of a motorized mechanism is sometimes required to achieve a fast slewing rate combined with a slow, braked approach to the final stopping point. To realize this combination two different speed motors are coupled as an in-line pair separated by a clutch. The speed of each motor is chosen to correspond to the required fast and slow mechanism slewing rates.

The fast motor has a double-ended shaft with one shaft-end directly coupled to the driven input of the operating mechanism. The opposite shaft-end of the fast motor is coupled via an electric clutch to the slow motor. For slow speed operation the slow motor alone is energized and thereby drives the mechanism through both the clutch and the fast motor, which'rotates at slow speed. For fast speed operation the clutch is disengaged by energizing its operating winding with a 24 volt D.C. supply. This isolates the two motors and allows the fast motor to drive the mechanism independantly.

Junctions Boxes - for two speed drives a special large junction box is used for the two motors. This has some different internal connections and also contains a relay as shown in Fig. 3.3.4-A. The 24 volt clutch operating supply is brought out of the junction box on a separate cable and gland connection. Because of the relatively high operating current required by the clutch (more than 1 amp.) a relay is included in the junction box to drive the clutch operating winding. A 24 volt signal from the MCB, fast motor terminal 12, is used to activate the relay whenever the fast motor is energized. The relay contact then connects a 24 volt supply to the clutch output line and disengages the clutch. Fig. 3.3.4-B shows a Large Junction Box for slow and fast motor with clutch. Linear Action Motor

All linear action motors incorporate their own normally closed internal limit switches, F3, F4. When the complete linear travel of the motor is used these internal limit switches are used in place of the normal Fl, F2 limit switches. When the full motor travel is not used, external Fl, F2 limit switches are fitted to the operating mechanism.

Fig. 3.3.5 shows the small junction box that is used with linear motors and the internal connections that are made when Fl, F2 limit switches are used. The Fl, F2 external switches are wired in series with the F3, F4 internal motor switches. Fl is wired in series with F3, and F2 is wired in series with F4.

F3 and F4 have a common connection and this is wired to terminal pin 1 (+ 24 volt supply) . In order to form the series switch connections two links are made as shown. The wiring between the terminal block and the Hirschmann socket is altered slightly as indicated on the drawing ; Hirschmann socket connections 15,3 are wired to terminal block connections 13,1 respectively. In standard junction boxes each connection on the socket is wired to the same number connection on the terminal block.

Exact details of wiring variations such as these can be found by referring to the appropriate drawing in a old paper folder, DWGS. VII

1.5.3 Introduction to the Motor Control System Manual and Computer Control Modes (Refer to Fig. 3.4.1)

All MCB switched motors are controlled locally by a motor control box (MCB). Each standard motor control box (MCB8) is capable of driving up to seven motors. The MCB is controllable in two primary modes, either by the computer (ON-LINE), or by manual command from various sources (OFF-LINE) . Operation ON-LINE or OFF-LINE is selected by manual command locally, or remotely from the control room. The selected state is transmitted to the computer in either case. It is also possible to bypass the MCB and to control the motor directly, on the spot, using a portable HAND-DRIVE box to supply the motor, see Section

Computer commands to the MCB are simple two state digital signals identified as follows - ON/OFF, LEFT/RIGHT and SLOW/FAST (when applicalbe). LEFT/RIGHT may also be interpreted as up/down or out/in depending on the direction of movement of the particular motor concerned. In the case of SLOW/FAST commands the computer is in fact controlling two mechanically coupled motors to obtain the two different speeds. In these cases the three different computer command signals - ON/OFF, LEFT/RIGHT and SLOW/FAST must be interlinked electrically within the MCB to derive individual control signals for the two motors, see old paper documents Part 2, Section 3b.2.9 for exact details.

In addition to controlling the motor, the computer may sense the motor status, even when OFF-LINE operation has been selected, by detecting the state of the limit switches. The computer can also determine whether the MCB is ON LINE or OFF LINE. When absolute position encoders are fitted to measure the intermediate position of the mechanism, the output signals are transmitted directly to the computer for processing. All computer command signals enter the MCB through optical isolators as simple ON/OFF signals.

When OFF LINE operation is selected the motor can either be controlled by a pair of manual push buttons within the MCB itself, by a remote control handset or by a pair of remote push buttons in the control room. The two different manual commands are identified as: - MOVE LEFT (or up/out) and MOVE RIGHT (or down/in). The motor is stopped automatically when a limit switch is reached (or if the pushbutton is released) and an indicator lamp in the pushbutton is illuminated. In the case of manual SLOW/FAST commands the two different speed motors are controlled by two pairs of manual pushbuttons, one pair for each motor. There are thus four different manual commands for a two speed drive: - MOVE LEFT FAST or MOVE LEFT SLOW, (or up/out), and MOVE RIGHT FAST or MOVE RIGHT SLOW, (or down/in). The Portable Hand Drive Box
(Refer to Fig. 3.4.2)

All motors, together with their limit switches, are wired to a junction box close to the motor. A 16 pole Hirschmann socket on each junction box connects it via plugs and H3 type cable to the appropriate MCB. In order to operate the motor directly, bypassing the MCB and its interlocks, a portable HAND DRIVE box may be plugged directly into the Hirschmann socket on the junction box. This allows direct, on the spot operation of any single motorized mechanism in emergencies, or for maintenance checks.

Fig. 3.4.2 shows the circuit diagram of a HAND DRIVE box. The unit is equipped with an input supply lead which must be plugged into a 380 volt, 3 phase supply socket. A transformer, bridge rectifier and smoothing capacitor, connected between one of the phases (R) and neutral (Mp) , provide an internal 24 volt D.C. supply for operating the internal control relays. The live transformer supply line is fused at 0.3 amps. Each line of the three phase motor supply (R,S & T) is fused at 1 amp.

Two relays, labelled Fl, F2, are supplied with 24 volt power via the Fl, F2 limit switches of the motor which is being driven. These limit switches are of the normally closed type. Provided the motor is not at the end of its travel, in either direction, both relays are activated to permit the motor to be energized in either direction.

When either of the motor control relays Rl or R2 is energized they supply the motor with power and cause appropriate movement of the motorized mechanism in one direction or the other. These relays are energized by a three position, center off switch on the hand drive box. A RIGHT command switches the 24 volt supply across motor control relay R2 to energize it. Relay R2 contacts connect the three phase supply (R, S and T) onto the motor supply output connections (6, 7 and 8) to cause movement of the mechanism in one direction.

When motor control relay Rl is energized by the selector switch the phase of two connections (S and T) is reversed, causing movement of the mechanism in the other direction. When the mechanism reaches the full extent of its travel in either direction the appropriate normally closed limit switch, Fl or F2, is tripped. Relay Fl or F2 de-energizes and removes power from its corresponding motor control relay, Rl or R2. The supply to the motor is then removed until the opposite direction of travel is selected by the three position switch. When either limit of travel is reached an indicator light, Fl or F2, is illuminated by additional contacts on the Fl, F2 relays.

When a two speed motor drive is to be controlled by a HAND DRIVE box each motor must be controlled individually. Two 16 pole Hirschmann sockets are provided on the junction box of a two speed drive, one for each motor. The HAND DRIVE box can be plugged into either one of these connectors, depending on the operating speed required. When the FAST motor is to be used the clutch separating the two motors must be disengaged. This is done with another switch on the HAND DRIVE box. This switch connects a 24 volt supply to the clutch operating line when either of the motor control relays, Rl or R2, is energized.

When the HAND DRIVE box is being used to control linear motors the state of the internal limit contacts F3, F4 is displayed on built-in indicator lamps. The two diodes in the clutch supply lines prevent the motor control relays Rl, R2, from being held on by the F4 contact if an operator switches the clutch key on in error. Motor Control Box Safety Interlocks

Although the general safety interlock systems of the lock systems directly concern the operation of the motors and telescope are functionally described in Section 4, the inter- their control boxes (MCB's). The general safety interlock system is not constructed as a one piece unit. Every motor control box contains a logic panel which is a part of the interlock system. This panel defines the logical conditions which must be satisfied before a motor is allowed to operate. Motor control interlocks are functionally described in Section 4.2.

All standard MCB's contain a special relay, labelled as the "B" relay, for each motor which they control. This "B" relay must be energized by the interlock system before the relevant motor can be operated. ĚThe "B" relay is the point at which the operation of the motor control circuits is distinguished from the operation of the interlock systems. If the "B" relay is de-energized the appropriate motor function of the general safety interlock system must be examined. A visual indication of the "B" relay status is provided. This is a green light positioned between every pair of control pushbuttons for each motor.

The end positions of the motorized mechanisms, as determined by their Fl, F2 limit switches, is in many cases a logical condition which affects the "B" relays of other motors. In these cases the Fl, F2 limit signals are re-transmitted out of the MCB as general safety interlock signals. Operation of the Standard Motor Control Circuit
(Refer to Fig. 3.4.4)

All of the motor control boxes make use of a standard circuit, with some minor variations, to control the switched 3 phase motors. Fig. 3.4.4 is a schematic drawing of the standard control circuit for a single motor.

3 phase, 380 volt power enters the circuit through a motor protection circuit-breaker at the bottom of the drawing. If the motor consumes excessive current the circuit-breaker trips out and must be manually reset. A single motor protection warning light in each MCB indicates when any of the motor protection circuit-breakers in that MCB have tripped out. All of the auxiliary contacts, for each of the motors controlled by a single MCB, are wired in-parallel so that each can illuminate the single warning light.

The B relay is energized by the general safety interlock system as explained in the previous section. Unless this relay is energized the three phase supply to the motor is interrupted to prevent it from operating. To provide a visual signal which shows when each motor has been enabled by the safety interlocks, a "B" indicator lamp is illuminated whenever the B relay is energized.

The two normally closed limit switches Fl, F2, which sense each end of the mechanism's travel, are shown at the top of the drawing. Each limit switch energizes a dedicated relay, also labeled Fl, F2. As both limit switches are normally closed types the Fl, F2 relays are normally energized unless the mechanism is at either end of its travel. Lamps Fl and F2 are illuminated when the mechanism reaches the appropriate limit switch. The limit signals Fl, F2 are also transmitted via series resistors to optical isolators in the computer interface

Movement of the motor in either direction is controlled by the two motor control relays Rl and R2. When it is energized one of these relays connects the three phase supply directly to the motor, without phase reversal, to cause movement in one direction. For movement in the opposite direction the second relay switches the three phase supply to the motor, but reverses two of the phase connections to cause movement in the opposite direction.

These motor control relays may be energized from three sources shown schematically on the drawing ; the computer command, the local pushbuttons which are mounted in the MCB itself and remotely from a portable handset or the control room. All of these command sources are prevented from energizing the R1 or the R2 control relay if the corresponding limit relay, F1 or F2, is de-energized. For example motor control relay R1 cannot be energized if relay F1 is de-energized. This would mean that the motor had reached the end of its travel and the F1 limit switch had opened.

To prevent relays R1 and R2 from being energized simultaneously an auxiliary contact from each relay is wired in series with the operating coil of the other relay. If control relay R1 is energized an auxiliary contact in series with the operating coil of relay R2 opens, preventing R2 from being energized. These relay interlocks are necessary otherwise it would be possible for both relays to be energized simultaneously causing a short circuit across one pair of the incoming 3 phase supply lines. The Computer Interface
(Refer to Fig. 3.4.5).

Fig. 3.4.5 is a more detailed drawing of the standard motor control circuit which includes the computer interface. For controlling a standard motor there are only two command signals from the computer, OFF/ON or LEFT/RIGHT. Left/right may also be interpreted as either up/down or out/in depending on the direction of movement of the mechanism which is being controlled.

These two signals each drive an optical isolator, Motorola type 4N32, via series resistors to limit the input currents (rl) These optical isolators, or opto-couplers, consist of a gallium-arsenide infra-red light emitting diode (LED) which is optically coupled to a light sensitive transistor (photo-transistor). They are housed in an opaque plastic package and are unaffected by external light. The transistor is electrically isolated from the LED which allows the computer command signals to be electrically isolated from the motor control circuits. This is important to eliminate interference from ground loops and to prevent other interference being coupled into the computer lines.

The photo-transistors each drive a Siemens relay (Cl, C2). When the computer command inputs are off, corresponding to "OFF" and "LEFT" commands, there is no current flowing in the LEDs and the photo-transistors are cut-off. When one of the computer command inputs is on, corresponding to an "ON" or a "RIGHT" command, a signal of about 3.5 volts appears at the command input. This causes an input current of approximately 30 mA to flow in the LED, the photo-transistor saturates and switches on the corresponding C relay.

A + 24 volt supply is wired through the Cl contact to the pole of the C2 changeover contact. Depending on the command inputs, a +24 volt signal is generated by the C relay contacts and routed via either the Fl or F2 relay contacts to energize one of the motor control relays, Ri or R2. Left or right movement of the motor then takes place provided the appropriate Fl or F2 relay is energized.

Additional contacts on the Fl/F2 limit switch repeater relays are used to transmit the Fl/F2 limit signals, via series resistors (r2), to optical isolators in the computer interface. These signals inform the computer that the motor has reached the extreme of its travel in one direction, Fl or F2. General MCB Interface Connections
(Refer to Fig. 3.4.5)

Fig. 3.4.5 illustrates the standard motor control circuit for one motor but give more detail on the various input/output connections than the previous schematic control circuit.

COMPUTER INTERFACE CONNECTIONS - All command input signals from the computer, and Fl/F2 output signals to the computer, are wired to two Hughes 88 pole sockets (HGS 1 and 2) on each MCB.

MOTOR OUTPUT CONNECTIONS - All MCBs have one 16 pole Hirschmann socket (H16) for each motor that they control. This connector carries the three phase, 380 volt power output lines to energize the motors and the Fl/F2 limit switch connections.

REMOTE CONTROL INTERFACE - A 48 pole Burndy socket (B48) on the front door of each MCB allows the unit to be controlled remotely, either from the remote control handset or from the control room.

The ON LINE/OFF LINE signals enable either computer or manual control of each MCB as explained in Section 3.4.1. These 24 volt signals are generated locally in each MCB and enable either the C-relay contacts (ON-LINE) or the manual push buttons. The "OFF LINE" or "MANUAL" signal is also wired to the Burndy 48 pole socket so that the appropriate remote manual control source is enabled during OFF LINE operation.

Although the relevant connector is not shown in Fig. 3.4.5 each MCB is supplied with 3 phase power through one additional 16 pole Hirschmann socket. The input power lines are then connected directly through an input circuit breaker before they are wired to the separate motor control circuits (these connections are shown on Fig. 3.4.5 as the three input phase connections T, S and R) . This input circuit breaker has differential current sensing to detect earth leakage currents. An earth leakage current of more than 30 mA will trip the circuit breaker and isolate the MCB to protect operating personnel.

The 16 pole Hirschmann socket which is used for 3 phase power input to each MCB is also used for the MCB to MCB interconnections required by the general safety interlock system. The Hirschmann plug which feeds this socket is wired with type 113 cable. The five screened inner conductors are used for the 3 phase supply while the outer 11 conductors are used for the safety interlock connections. The Remote Control Hand Set
(Refer to Fig. 3.4.7).

This portable pushbutton handset is used to operate a motor control box remotely using a plug-in cable. The handset should not be confused with the portable hand-drive box, previously described in Section, which is used to control a single motor directly. The remote control handset may be plugged into the 48 pole Burndy socket on the front door of an MCB unit to control all motors which are controlled by that MCB unit (7 in the case of a standard MCB8) . The unit requires no external power supply as all its controls and indicators operate directly in parallel with their counterparts in the MCB.

Fig. 3.4.7 shows the internal wiring of the handset. For each motor there are a pair of Fl/F2 pushbuttons, a pair of Fl/F2 indicator lights and a "B" indicator light.

The Fl/F2 pushbutton units house their respective Fl/F2 indicator lights within the same assembly. These two integrated pushbutton/indicator assemblies and the "B" indicator light for each motor are physically grouped side by side, with the "B" indicator light at the center. As a maximum of seven motors can be controlled there are seven such groups of controls in each handset.

All controls and indicators are wired in parallel with their corresponding controls and indicators in the MCB unit, refer to Fig. 3.4.4. The Fl/F2 pushbuttons correspond to the remote LEFT/RIGHT pushbuttons shown in Fig. 3.4.4. The Fl/F2 indicator lights are wired back in parallel with their counterparts, similarly labeled on Fig. 3.4.4. They indicate that the motor has reached the limit of its travel in one of the two directions. The "B" indicator lamp is similarly wired and is illuminated when operation of the motor has been enabled by the general safety interlock system.

Detailed operation of the ON-LINE/OFF-LINE selector button is described in old paper documents Part 2, Section 3b.2.8. This button is used to select either ON-LINE or OFF-LINE operation. Depressing the button once causes a change of status from ON-LINE to OFF-LINE or vice versa. The handset can only be operated in the OFF-LINE or MANUAL mode. This state is confirmed by the corresponding green light which must be illuminated. Remote Control from Control Room

Manual pushbuttons in the control room may also be used to control an MCB remotely. Cables from the control room pushbuttons are normally wired to the 48 pole Burndy socket on the front door of each MCB. Front panels in the control room racks carry all the pushbuttons and indicator lamps which are required to operate each MCB. There is a separate front panel for every two MCB's that are controlled.

More details can be found in the Engineering Panel Section.(Chapter 3, Alpha and Delta Drives)

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