IE902596A1 - Monitoring and control of oil/gas fields - Google Patents

Abstract

An oil/gas field system for monitoring certain characteristics in an oil and/or gas field and for controlling certain operating equipment in the field containing: a sensor (9) measuring the characteristic and for generating a signal (8) corresponding to a value of the characteristic; servo devices (11) for controlling the operation of the equipment; programmable logic (5) connected to a certain number of said sensors (9) for receiving the signals (8) of the sensors (9), the logic device (5) having outputs connected to the servo devices (11) for automatically changing the status of said equipment controlled by the servo devices when the input electrical signals are outside some allowed range remedy a non-complying condition of the equipment; and control computer remote from but connected to the logic for establishing the allowed ranges in the logic and for establishing control signals in the logic device for controlling the output of the logic device to the servo means.

Description

The present invention relates to on site and remote monitoring- and control of oil and gas operation.

Oil and gas production installations are typically monitored and controlled ty installing on site standard sensor devices, such as pressure gages, flow meters, overflew indicators, vibration switches, etc. on the equipment. Operators can thus determine the status of the production equipment and wells by visually checking the sensing devices. The seniior IQ devices connected to critical equipment are usually wired directly or through electrtroechanical relays to shut off control devices which can interrupt the operation of non complying equipment or shut off the whole production facility if dangerous conditions occur. Curing normal operation the operator has to read the various gages or sensor devices and make the appropriate manual adjustments on well valves, production equipment controls, etc. to maintain the oil or gas well or field within acceptable operating parameters.

The number of sensor and control devices is a function of the complexity of the installation, operating requirements, the prevailing operating practices of the field operator and the need to comply with statutory safety requirements.

It is relatively catmon, even in the simplest installations, to have a number of cut-off sensors (such as stock tank overflows, engine oil le/el and pressure, etc.) which disable or turn off seme of the equipment or shut off the well when the pararetars monitored exceed critical levels,.

SB9720US IA In mere sophisticated ir^tallaticns the outputs of sene or all of the sensor devices are brought to a central panel where the operator can monitor the operation of the field and the equipment. This avoids the need to gather information on location and the operator can perform his duties more rapidly by only going to the locations or equipment needing intervention.

A further level Of autonation is added when servo controls; i.e. electric motors, pneumatic activators, rheostats, etc., are added to key equipment or wells and can be activated by the operator from a remote io location (i.e. the panel roan) and bring the operation of the equipment into compliance. More sophisticated installations use control theory Ϊ techniques and open or closed loop circuits to drive, with a function MUch more complex and expensive monitoring control systems are also in use. SCADA (Supervisory Control and Data Acquisition) systems available commercially and utilized mostly in off-shore operations are capable at monitoring remote operations through sensors which report to a central monitoring location through a ccnrounication satellite link. In a scacA installation the sensor and control devices must be progranmed an site In case of a non-complying condition, the output of the on location sensor is relayed, via satellite, to the central monitoring location. At the central location a processor or the human element makes a decision on a corrective action which is then relayed, again via the satellite link, SB9720US - — ΛΛΟΓΣΙΙΚ __ it to the remote locaticn servos.

In the present invention the outputs of commercially available or custom analog or digital sensors are connected to one or more ocnwerciaiLly available programmable logic units. The outputs of the logic units are connected to either ccemercially available or custom servo mechanisms which respond to the output of the logic units as a function of the outjput of the sensor devices ftnd thus can take action on the monitored equiptn^rt to comply with the preprogrammed instruction. Once the monitoring devices are connected to the inputs of the programmable logic units and the servo mechanisms are connected to the output of said programmable logic units, the operator can program both the compliance intervals for each sensor and the desired response by each servo iron a commercially available contrdl computer and software which is connected to the programmable logic units either through a telephone link or a digital data link. The programmable logic units will be capable of both monitoring and automatically correcting the non conplying condition or shutting down the equipment without need of operator intervention or the reed to ocmmunicate with -a remote control locaticn such as in the SCADA system. The system is thus immune from failure in the oanmunication link and greatly improves safety and reliability. Once the programmable logic unit has taken an action, it can be programmed bo report the event both on site and in the communication link to the control computer. The programmable logic unit is also capable of reporting system status on a recurring basis and loc' the output of all sensor devices for later analysis.

SB9720US Given the almost total flexibility in the number and type of sensor devices, servo devices and the programmability of the interaction between the two sets of services, the system is capable of monitoring and controlling automatically essentially all phases of an oil or gas production facility.

Summary of the Tnventinn One object of the invention is to monitor the operating parameters tf an oil or gas production facility and control its operation through thfe use Of existing sensors, servo devices and programmable logic units.

Another object of the invention is to allow the operator the flexibility of changing operating parameters by making changes through software program without need to change the hardware installation on tie production facility.

A further object of the invention is to receive status reports on the operation in an efficient and economical manner.

An additional object of the invention is to be able to change the operating parameters of the installation Iran a remote location through commercially available software and hardware.

In the preferred embodiment, the foregoing objects are achieved by the 2ύ means described below.

Sensor devices with analog output meeting the standard 4-20 mA outpht or αη/off sensor devices are installed conventionally throughout the oil or gas production according to operating and safety requirements, ihe output of such devices is connected to a local programmable logic unit C’LiU’’) such as the Ncvar Controls Corporation Executive Processor or SB9720US controller. Uve LLU is equipped with a number of input ports which can interface with the output of the sensor devices. As shown in Fig. 1 each sensor devices are connected to a corresponding input port of the LIU. Given the physical irput bus limitation which exist in the UU, if additional sensor devices need to be monitored, the system is expanded by connecting, via a standard RS485 connector, the LLU to one or more renote logic units (RIXJ) art as the Ncvar Input/Output modules. The possibility of adding RLUs allows to increase the number of monitored points and the number of control devices to handle even the most ccmpljex installations.

The LIU is equipped, among others, with internal clock, RCM mamorie|s for its management and RAM memories for the acceptance of operational instructions (setting of ram logic states) which can be, inputted, via an internal telephone module or a data link, frttn a control ocmputer typically located at the hone office. The control computer, such as the Engineering Support System of Ncvar Corporation, is a personal computer or mini computer containing proprietary interface equipment and. software capable of loading the operational parameters required by the installation into the RAM memories of the LLU. In larger installation^ requiring RIl's, the instruction for the RAM memories of the RLUs is transferred from the control computer to the LLU RAMS which then transfers the instructions to the RLUs RAMs via the RS485 bus. RLUS can thus communicate back and forth with the LLU tut not directly with the control computers.

SB9720US Trie Lib and the ΜΤ'ε can thus be programed to perform the following, function: 1. ) Data lotxrijq. The Ui and RXUs read the output of the senjsoir devices, store it and can transmit the data, via the ocrommieation link to the control ccxtpjter. The data is also available on site through a control panel and display installed on the ECU. 2. ) Fault Detection. Both the LIE and the RIEs can be programmed to detect a fault condition which exists when the output of a sensor device falls outside a preprogrammed allowable range, when a faulty or non complying condition is detected, the unit detecting the non ocaplying signal, will respond according to the programmed instruction by activating one of its outputs connected to the appropriate servo device. 3. ) Corrective Action. The local and remote logic units are capable of two types af output: a. on/off a.c. voltage. b. pulse modulated a.c. voltage.

The on/off a.c. voltage can be used to activate a servo, such as a shut-off pneumatic valve to shut off the well or a cut off switch, to kill an engine if the non complying condition requires such action.

The pulse modulated a.c. voltage is a function of the value of the sensor output and thus can be utilized in a closed loop circuit to drive a servo mechanism which will act on the process until the sensor output Ijias returned within the allowed operating range. 4. ) Reporting Function. The local logic unit can be pi to report to the control computer, via the ccmwication link, either it SB9720US preset time intervals or upon occurrence of a non ocnplying condition, the Status Of the system. Both the on site operator and. the operator of tha control ccanpjter can poll the LUJ to determine system status.

Since the system dees not depend on the functionality of the 5 ccsmnunication link to operate once it is progracmed. and all decisions are made on site by the LLU or the RHJs, reliability and safety are greatly improved.

The system capability to accept both digital (on/off) or analog irpe and to be programmed fibr both on/off and analog (proportional) output 10 signals makes it possible to essentially monitor all phases of the operation and take all manners of corrective action for a total or partial operation management, as desired by the operator. 3B9720US BRIEF DESCRIPTION OF THR DRAWINGS Fig. i Fig. 2 Fig. 3 Is a block diagram of an installation including «11 type* of Input and output which can be included in the system.

Is the representation of an actual installation in the field.

Ia the flow chart . of the control logic activated by one of the sensors.

OiyitXfTIOW qr IBS pkitbubsc SHBODIMSWT ?1j. 1 is the black diagram at tha interconnection a:' a typical systsm elbowing the basic system component a according to the preferred embodiment commercially available computer, Corporation Engineering Support System Control Computer 1 li • uch aa the Noyar which contains buffer hardware and specialized software to control the system The control computer is connected to a video display 2 and, if desired, can be connected with a compatible printer 3 Components 1,2, and 3 can be located anywhere access to a teleohone line is available.

The central computer is the balance of the system which to be monitored and controlled. connected, via a telephone link J to ie installed on the location LLU 5, which ia a commercially available logic processor, connected, via an internal modem and link 4, to the conf computer i, LLU 5 may also be connected, via an R3435 is rol bus S, to one or more RLUe 7. The addition of RLU units, which are commercially available programmable logic units, such as the Novar Corporation Input/output modules, allows the system to be expanded to handle all of the monitoring and control function* neceseary in the installation. 3oth the LLU and RLU units are connected, via input buses 8 with monitoring sensors 9. The sensors ar· installed on the equipment to be monitored. The number of sensors which can be connected to each unit is typically limited to eidht. Said sensors can either be of the on/off type) or commercially available 4-20 mA output analog sensors.

The LLU and RLU units are also connected via output buee^ 10 to servos li. These commercially available devices car be on/off devices or proportional analog devices. The servos are also Installed on the equipment. depending on] the instructions received from the LLU or the RLUs, they either shut off or alter controls or settings on the controlled equipment. The LLU may also be connected, via a data bui 12 to a local printer- 13. Once the installation is complete, the operator sets the normal operating parameters for I aid sensors in the control computer. Thi3 sets the complying and noncomplyihg output range for ail the sensors in I the installation. Next the operator sets the desired response for all msors amors settings function of servo units ll as a the total response and established. The logic lei are then loaded into The C.LO transfers the lo< The installation is ti The C.LU and RLTe need 9. Thus and servos is ., in tha control computer LL'J S via telephone link 4. Th levels to the RLOe via data bus 6. 4? 4 1 * ? « « M M« MM «4 «Μ ?} the output interaction lCV9+& v- J ’’•{IB i\AaUW VXCl WU9 Q· 4 uB ^ΙλΒ^ϋ fully programmed and operational. The C.LU a; further instructions from control computer i and w perform all monitoring and controls unattended. The will report system status to control computer l on demand at eet times, as programmed from the control computer.

I Fig. 2 ie the physical installation diagram of an actual system and is representative of a typical medium size installation. The installation consists 4 RiVs (102,103,104, and 103) in Fig. 2 of one LiU 101 und The are numbered installation in Fig. 2. installation also includes thirteen sensors. The senebre 106 through 118 in* Fig. 2. In addition the servos numbered 119 through 123 utilizes five pg3CRi?Tioy or saxgoRs Sensor 106 is a temperature sensor which is installed at the glycol feed into the glycol tower. It is a 4-20 mA outout device, such as an Omega Inc. K Thermocouple, Sensor 107 la a fluid level sensor with 4-20mA output (Omega LV110I Sensor 108 is a flow meter used to meter the out of the stock tank. Sensor 109 i 20mA output) capable of detecting full and cannot store additional oil. Sensor 110 is a fluid level sensor (4-20 mA) capable of detecting the leyel in the salt water tank of the salt water used for injection into the formation. Sensor ill is a pressure eeneor (4)-20 mA),such as Omega PX714, measuring the preseure of the waiter being injected into the formation. it is installed at the output of the injection pump. Sensor 112 is a 4-20 mA sensor installed In the engine lubrication loop to monitor engine oil pressure. Sensor 113 is a temperature sensor (4-20 mA), such ae TX-72 by Omega Inc., installed on the treater to monitor treater temperature. Sensor 114 is a 420 mA overflow sensor, such ae L73001 by Omega In installed on the treater to sense an overflow conditi Sensor 115 ie an overheat sensor, such ae TX-72 by Cm installed on the treater to detect an overheat condition. Sensor 116 is a pressure sensor (4-20 installed on the treater. Sensor 117 is installed on tne oil delivered a an overflow sensor 14whan the stock tank is a level sensor, such as LV1101 ______ ____ fluid level in the scrubber tower.

Sensor 118 is a temperature tensor (4-20mA) measuring the flare scrubber. I Cmega, determining t ie the temperature of the flare. gERVQ$ OE3CRIFTIOK Servo 119 is a 3 way mixing valve by JfATCO Corp, driven by a 1/2 horsepower electric motor which can mix hot and cold glycol to achieve the desired temperature before it is sent to the glycol tower, Servo 120 is a cut off switch which ehorta the magneto of the salt water pump engine. Servo 121 is « pneumatic valve installed on the wellhead which can turn the oil flow off, Servo 122 is a heater heating the treater unit, Servo 123 is a relay which drive» the lighting facilities at the installation.

DESCRIPTION 0? OPERATION The operating range of the sensors and the response of servos is loaded into the LLU and the four RLUs from Control computer, Ths operation, operating ranges for sensors and servos' responses are as described below. tie the the The glycol heater temperature sensor 106 is connected to R 102. The allowed operating range ia lass’ plus or minus 3 As the temperature falls outside the normal range t electric motor of servo H9, activated by RLU 102, adjus the 3-way mixing valve and the mix of hot and cold glycol maintain the desired glycol temperature in the glycol towe ie :s :a Liquid level sensor 107 is connected to RLU 103 and an empty oil tank condition. •ports Turbine flow meter 106 measures the oil delivered out of stock tank, once delivery takas place RLU 102 monitors delivery and the pre-loaded program converts the flow barrels. The amount delivered is printed on site relayed to the control computer. th ti, int ar d d a a h u d Level overflow sensor 109 is installed on the stock tank ar is connected to Riu 103. The RLU is programmed to allow maximum oil level off 13ft. When the oil level exceeds th allowed maximum, RLU 103 activates the engine cut off switc 120 and water injection in the field is discontinued. RL 104 also activates the well head pneumatic valve 121 ar shuts in the well. An alarm is printed on the printa connected to the LLU - and the LLU informs the contra computer of the condition. system (seconder y the salt wata The pre-loade specified range The operation of the salt water injection recovery) is monitored and controlled b level sensor 109 and pressure sensor HO. program allows the tank level to be in a If the output of sensor 110 is within the pre-ee tabl i ahid limits, the injection pump is operating. If the sensor output is outside the defined range RLU 103 will shut o: the injection engine by activating shut-off servo izo whi^h grounds the engine magneto, Injection pressure 111 is pressure reading servo with 4-20 mA output. The allowed pressure range in psi, le pre-programmed. if operating injection pressure is within the allowed range operations are normal. If the injection pressure falls outside the allowed range, RLU 103 again activates shut off servo ijo and gives an alarm to the operator.

The treater ia monitored by four aansors; 113,114,115 aid 116. Sensors monitor ars all 4 to 20 mA sensors and monitor temperature, overheat, overflow and pressure. The allownd range for the temperature sensor is 147 to 150 ?, At startup RLU 104 will activate servo 122 (heater) and the heater will operate until sensor 113 has an output within tie allowed range. The heater is then turned off. If an overflow or an overheating condition is detected by 114 or 115 respectively, then the heater ie turned off by RLU 104 and tine LLU will give a written alarm to the operatos Pressure 3ensor 115 monitors the pressure in the treater tank and alerts operator if pressure exceeds the preset allowed limit.

The flare scrubber has a level sensor 117, If liquid detected above the allowed level, the well is shut in by t activation of well shut off serve 121 connected to RLU 10 The operation of the flare temperature sensor described ijn more detail in the description of Fig. 3.

Fig. 3 is the logic flow chart of the operation off one the sensors, specifically the flare temperature sensor ills of Fig. 2, The flow chart indicates the interaction between the temperature sensor, the program logic leaded in the LaU and the RLU and the applicable eervos consisting of tHw wellhead pneumatic valve (121 in Fig 2) and the site The flow chart atart-up which Is lighting system, operation at flare procedure. A simplified flow chart state operation. details the systsjm the more complicated applies during stead At start-up the flare is ignited (Block 201). The syste automatically waits for a preprogrammed period 0 approximately 8 minutes to allow the flare temperature t heat up (Block 203) . After euch time the RLU 1Q5 to whic the flare temperature sensor is connected monitors th temperature (Slock 203). If the temperature is within rang no further action is taken (Block 205). If the temperatur is not in range the flare is pulsed and after one minut (Block 204) the temperature is monitored again by the RL e e e e for temperature increase (Black 206). If temperature increasing it is checked again, for proper range (Block and if It is within range the system takes no fuj action. If the temperature is not within range the proc is repeated. If temperature is not increasing the activates three servos. Servo 121 (wellhead pneuma valve) is activated and shuts the well in (Black 206) . location lights are turned on if the emergency occurs night (Block 209) and the injection pump engine is shut The RLU, via the LLO also informs (Slock 210) the cant computer (Block 213) via telephone (212), and prints emergency condition locally for the operator (Slock 211). Similar logic flow diagrams would be applicable ίο other sensors and servos. is «) further S3 LU lo he at 2C of rto tjh tie The preferred embodiment of the invention has been deecrib above, but variations and modifications within the spirit the invention may occur to those skilled in the art to whi the invention pertains.

Claims (12)

1. An oil/ga® field system for monitoring certain characteristics in an Oil and/or gas field and for controlling aertain operating equipment in the field, said system ccnprising: 5 a sensor operatively connected to the source of each of said characteristics, said sensor measuring the characteristic and for generating an electrical signal corresponding to a value of the characteristic; servo means operatively connected to equipment related to the 10 respective characteristic for controlling the operation of the equipment; programmable logic means having inputs electrically connected to up to a certain number of said sensors for receiving the electrical signals df the sensors, said logic means having outputs connected to said servo means for automatically changing the status of said equipment controlled by said 15 servo means when the input electrical signals are outside some allowed' range remedy a non-complying condition of said equipment; and control computer means remote from fcut electronically connected to iaid logic means for establishing said allowed ranges in said logic means amd for establishing control signals in said logic means controlling the 20 output of said logic weans to said servo means.

2. An oil/gas field systen of claim l wherein said logic mea^is comprises a remote logic unit for receiving electrical signals from up to a certain number of sensors and for changing the status of the respective SB9720US servo means When the electrical signal from the sensors is outside an 5 allowed range, and a local logic unit operatively connected to up to a number of said remote processors and to said control ccnputar unit, said remote logic unit and said local logic unit responding to said electrical signals by controlling the respective servo means, and said local logic unit receiving signals iron said control unit for changing said ranges and 10 for controlling the servo means, said local logic unit transmitting signals from said control oonputer unit to said remote logic units.

3. For use in an oil field comprising at least same of an oilwell, flow line(s) running from the well to a treater tank for removing water from oil, a separator tank for holding oil to be separated from gas, flew line(s) for transferring fluid from the treater tank to the 5 separator tank, a flare stack for igniting the gas, flew line(s) from (the separator tank to the flare stack, stock tank(s) for storing oil from (the well, flow lines to the stock tank(s) , pump(s) for injecting liquid irfto the ground to aid in the extraction of oil from the well, purtp(s) for pumping oil to the stock tank(s); H^S detection means? actuation means 10 for controlling the Well's) and the pump(s) ; and servo means for operating the actuation means; a monitor and control system comprising: sensor means, including at least seme of the following: well pressure sensor means for generating electrical signals 15 to corresponding pressure of oil flowing from the weii(s) flew meter sensor means in at least seme of the flow line(s) SB9720US for generating electrical signals corresponding to flew of oil in the respective lines; treater pressure sensor means for generating electrical signals corresponding to the pressure in said treater tank(s) ? separate^· sensor means for generating electrical signals corraspqpding to the amount of liquid in said separator tank(s); flare sbhek sensor means for generating electrical' signals OOrrespcpding to the temperature of the flare produced iij said flafce stack; senspr means for generating electrical signals oorrespehding to the presence of an amount of gas; pump engine pressure sensor means for generating electrical signals corresponding to oil pressure (s) in the engine of said punp; pump gear bcoc pressure sensor means for generating electric* 1 signals corresponding to the oil pressure in the gear box(es) of said punp(s) ; vibraticti sensor means for generating electrical signals corresponding to the vibration of said punp(s) ; and t^nk· level sensor means for generating electrical signals corresponding to the oil level in said stock tank(s); SB9720US programmable logic unit, means electrically connected to said 45 sensor means and to the servo means for the well(s) and the pump(s) fori Changing the status of the well(s) and the purop(s) in response to said respective electrical signals of said sensor means exceeding certain range values; and control ULUpiOer means electronically connectable to said logic: 50 means, means for inputting into said occ^xiter means the range values for the sensor means and the signal levels to the servo means in response to the electrical signals, and means for transferring said range values and said servo signal levels to the logic unit.

4. The monitor and control system of Claim 3 wherein said logic unit means emprises: at least one remote logic unit connected to at least some of s^id sensor maans and to said servo means; and 5. At least one local logic means operatively connectable to at l*ast one of said remote logic units, said local logic unit transferring the range values and the signal levels to the servo means to the remote logic units, and said local logic means having display means for displaying signals from said local logic means and firm said remote logic means.

5. The control and monitor system of Claim 3 and further including: SB9720U3 a link between said control ccnputer system and said logic said link transmitting range values and signal levels for controlling servo means from said control ccnputer system to said logic means. means the 10

6. The monitor and control system of Claim 4 and further including printer means connected to said local logic means for printing the processed signals fraa said sensors.

7. A method for monitoring and controlling devices in an oil field, said devices including at least some of the following; well(s) for the oil; treater tank(a) for separating water frcra the oil; 5 separator tanJt(s) for holding the oil and gas or other liquids (to be separated iron the oil; flare stack(s) for receiving and igniting waste gas; poison gas detection means; stock tank(s) for holding oil drilled fron the ground; 10 punp(s) for injecting fluid into the ground to aid in the recovery of oil; pwps for transferring oil in the devices; flcx^ lines connected to the various devices for an oil production system; and 15 sensor means connected to the respective devices for sensing afid generating electrical signals corresponding to characteristics of the respective devices, the characteristics being indicative of a potentially SB9720US dangerous situation if they axe outside certain range values; 2U servo means for controlling the operation of the respective devices; at least one logic means connected to said sensor means far receiving the respective electrical signals from the sensor means and dor actuating the servo means to operate the devices; and 25 control computer means operatively connected to the logic meand by link means for inputting software program(s) into said logic means, said control canputar means beirg remote from the logic means, said method comprising: placing a software program into said control ccuputer system fdr 30 indicating ranges for the respective electrical signals from the sensor means, and for actuating said servo means when the respective electrical signals are outside their range values; link means for transmitting the software program frcm the control computer means into the logic means; and 35 display means connected with said logic means for reading sigrvp.s to said logic means. 3.

8.A system for monitoring and controlling devices in an oil and/or gas field, the devices including equipment for drilling, processing and storing oil and/or gas, the system including: sensor means operatively connected to the devices for generating 5 electrical signals corresponding to characteristics of the devices; 5B972CUS programmable logic unit means having inputs operatively connected t4 the sensor means, said logic unit means having internal clock means, RdM memories for the management of the logic unit means and RAM memories for the acceptance of operational states, and outputs; 10 servo means having inputs operatively connected to the outputs of siid logic unit means, and outputs connected to said devices for controlling the operation of the devices; ccmmunicaticn link means cperatiyely connected to said logic unit means; and 15 control computer means operatively connected by said contnunication tink means to said logic unit means, said control aanputer means having software for receiving the operational parameters of the RAM memories kni operational signal levels for the servo means and for transferring the software via said link means to said logic unit means, means for receiving 20 the sensor electrical signals, and display means for generating intelligible signals from said received sensor electrical signals; said logic unit means having default means for receiving electrical signals from said sensor means and for sending cut operating instructions signalg to said servo means to correct or shut down the devices according 25 to the values of said sensor electrical signals.

9. The system according to Claim 8 and further including data legging means connected to said logic unit means for receiving and stcring the sensor electrical signals and for transmitting said sensor electrical gjignais to said control computer means. SB9720US

10. The system according to Claim a wherein said logic unit lasane further includes reporting means for measuring an a recurring basis tho Status Of said sensor means and for reporting on a recurring basis said status to said control ocuputer means.

11. The system according to Claim 10 wherein said logic unit means includes programmable remote logic unit means operatively connected to said sensor means for receiving the sensor electrical signals and f^r sending out operating instruction signals to the servo means, and 5 programmable local logic means operatively connected to said remote logic unit means for transmitting operational parameters to said remote logic units and for generating operating signals to said servo means.

12. A system according to any of claims 1 to 6 or 8 to 11, substantially as described herein with reference to the accompanying drawi ngs.