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CONTROL INTERLOCK AND MONITORING SYSTEM FOR 80 KW IOT BASED RF POWER AMPLIFIER SYSTEM AT 505.812 MHZ FOR INDUS-2 Gautam Kumar*, R.K. Deo, M.K. Jain, Sunil Bagre, P.R. Hannurkar; RRCAT, Indore –452013, INDIA, Abstract For 80 kW inductive output tube (IOT) based RF power amplifier system at 505.812 MHz for Indus-2, a control, interlock and monitoring system is realized. This is to facilitate proper start-up and shutdown of the amplifier system, monitor various parameters to detect any malfunction during its operation and to bring the system in a safe stage, thereby assuring reliable operation of the amplifier system. This high power amplifier system incorporates interlocks such as cooling interlocks, various voltage and current interlocks and time critical RF interlocks. Processing of operation sequence, cooling interlocks and various voltage and current interlocks have been realized by using Siemens make S7-CPU-315-2DP (CPU) based programmable logic controller (PLC) system. While time critical or fast interlocks have been realized by using Seimens make FPGA based Boolean Co-processor FM-352-5 which operates in standalone mode. Seimens make operating panel OP277 6” is being used as a human machine interface (HMI) device for command, data, alarm generation and process parameter monitoring. separate isolated cabinet called HV deck. This in turn demands the high voltage isolation signal conditioning unit (SCU) to reproduce the sense voltage and current signals of auxiliary supplies at ground potential. Rated beam current is 3.3 A operated in class AB mode with quiescent current about 100 mA and there is no body current in this IOT amplifier system. The solenoid supply (7 V, 25 A typically) is needed to focus the electron beam travelling from cathode to collector, this supply is used at ground potential. Forced air cooling (3 cubic meter/minute, 2 kPa) is used for the cooling of electron gun and cavities of IOT tube, however collector & body of IOT tube are water cooled (50 lpm, 270 kPa) by low conductivity water (LCW). The arc detection and RF monitoring system is also incorporated with control, interlock and monitoring system. The high power IOT based amplifier system has been tested up to 50 kW RF power level. The set up is shown in figure 2 with its subsystems marked by number 1,2, 3,4 and 5. OVERVIEW OF IOT AMPLIFIER SYSTEM 80 kW IOT is a linear tube based hybrid device having partial features of triode tube and klystron. Figure 1: Internal structure of IOT tube. To achieve high power RF amplification biasing of IOT tube with high voltage (HV) (-36 kV rated but most of the test have been carried out at -32 kV) is needed. This high voltage will appear across the cathode and collector of the amplifier tube, where the collector remains at ground potential. Structure of IOT tube is shown in figure 1, this amplifier has electron gun auxiliary supplies floating at cathode potential -32 kV, namely, filament power supply (7.25 V, 25 A), sputter ion pump supply (4.5 kV, 1-2 µA), control grid power supply (-300 to -80 V, < 1 mA), these supplies are mounted on Figure 2: 80 kW IOT power amplifier system set up of Indus-2, here cabinet no. 1 is control, interlock and monitoring system, 2 is HV deck with optical isolation SCU, 3 is High power IOT amplifier, 4 is LCW cooling system and 5 is air blower. CONTROL, INTERLOCK AND MONITORING SYSTEM REQUIREMENT The high power amplifier is intended primarily for unattended operation under automatic or remote control. The control system controls the start-up sequence and maintains continuous surveillance over the operation of the equipment. This amplifier system needs to be switched on in a predefined sequential manner for the safe and reliable operation i.e. the first step is heating of filament called black heat mode (B_H) (stage I). Second step of filament heating is called standby (S_B), at this stage (stage II) cathode is ready for electron emission. In third step transmit (Tx) command is issued (stage III) to put on high voltage. After attaining -32 kV system issues an HV ready command (digital o/p) so that RF input can be given to IOT amplifier (stage IV). This control logic flows one by one in sequential manner from first stage to fourth stage. Voltage and current values of the auxiliary and focussing supplies have safe operating range. In this range the operation of IOT is normal and safe. If any value goes out of the safe range IOT amplifier system should be tripped or taken back to previous safe stage as defined in the control system program. Similarly there are several other interlock signals incorporated which have been processed and monitored continuously e.g.: coolant temperature interlocks; flow rate interlocks; beam voltage and current sense interlocks; door interlock etc. This interlocks are comparatively slow (execution time is of the order of ms). There are fast interlocks (execution time is of the order of few µs) such as RF excess input drive and excess RF output reflected signals, IOT and circulator arc. The monitoring system is needed to generate command signals and display set, read back and status signals of the power supplies flow switches and also display value of RF input (i/p), output (o/p) power and VSWR. This system should also takes care of alarm generation and fault logging. EMPLOYED CONTROL DEVICES programmed by using Simatic Manager V5.4 incl. SP5 software. Language used for programming is function block diagram (FBD) language. While the Arm controller based HMI is programmed by using Simatic WinCC Flexible 2008 SP2 software. PLC and HMI communicates via MPI cable by serial transmission while PLC and FM352-5 is interfaced via simple wire cable as shown in figure 5. Table 1: Specifications of employed devices S N 1 2 3 4 4 5 6 7 8 9 Device Name & Model Number CPU315-2DP 6ES7-315-2AG10-0AB0 Digital input (DI) module SM321-7- BH01-0AB0 No. of Channels - Signal levels 16 --do as-Digital output (DO) module SM322-1BH010AA0 --do as-Analog input (AI) module SM331-7KF020AB0 --do as-AI SM331-7HF01-0AB0 Analog output module SM332-5HF00-0AB0 FM352-5, 6ES7-3525AH00-0AE0 -do as-do as- Logic 0 (-30 to 5 V), Logic 1 (13 to 30 V) --do as---do as-- - -do as8 --do as-4-20 mA current 8 8 8 -do as0-10 V 0-10 V 11 DI, 8 DO Logic ‘0’ same as DI & ‘1’ (11-30 V) To generate control logic start-up sequence and slow safety interlocks CPU 315-2DP has been used with its S7-300 series digital and analog i/p, o/p modules as shown in figure 3. The high speed Boolean co-processor function module FM 352-5 is used to control and process all the fast interlock signals. It is FPGA based control system having digital i/p and o/p channels. CPU is connected to its input and output (I/O) modules via backplane bus. CPU and all the I/O modules and FM 3525 are operated by 24 V dc supply. All the devices of figure 3 are specified in table 1. Figure 4: Employed HMI device OP277 6” in IOT amplifier system. SCHEME OF CONTROL SYSTEM Figure 3: Employed PLC system and high speed Boolean coprocessor FM 352-5 in IOT amplifier system. FM352-5 (shown in figure 3 and also refer 9 number of table 1) and HMI Op 277 6” (6 inch) (shown in figure 4) is running independent from CPU. The arm controller based Op277 6” is a panel mounted device. It operates by 24 V dc supply. PLC and FM 352-5 is The organization of control system is done like decentralized control system (DCS) as shown in figure 5. A DCS distributes device control between a central process controller and local process controllers. In this scheme PLC works as central process controller while FM352-5 works as local process controller. PLC gets inputs from all other subsystems of IOT and according to stored program it updates its digital and analog outputs. In this way it controls the overall system operation. This amplifier system is able to operate from local as well as remote panel. Various operating parameters values of subsystems are given to PLC system via signal conditioning units (SCUs). These SCUs provide digital or/and analog signals compatible with PLC system. These signals are interfaced with the PLC system via its I/O modules and ultimately interfaced with CPU via backplane bus as shown in figure 5. HMI is used to log commands from local panel such as select local/remote (L/R) operation, system off, Reset, B_H on, S_B on, Tx on, RF on, RF off. It is used to set control grid voltage in the range -80 to -300 V by default this voltage is -150 V, whenever this voltage crosses defined range it generates alarm. It also indicates all the faults/interlocks. FM352-5 gets digital i/p signals such as HV ready, RF on and quiescent current status from PLC. It gets other digitals i/p signals such as IOT arc, circulator arc, excess i/p RF drive, excess RF reflected at o/p from RF SCU. FM 352-5 generates 2 digital o/p in which one is used to RF on/off for RF switch and other is used to HV off. CONTROL SYSTEM OPERATION Control operation is depicted in flow chart Figure 5: Employed s7- 300 PLC system in DCS scheme. Total signals incorporated are as following: 17 analog input signals are incorporated out of which 7 signals are 4-20 mA current signals (2 flow rate and 5 temperature monitoring signals). Other 10 signals are 0-10 V voltage sense signals out of which 6 signals are voltage and current sense signals of electron gun auxiliary supplies. Other 2 signals are voltage and current sense signals of solenoid power supply. Remaining 2 signals are sense signals from beam voltage (from potential divider) and beam current (from hall sensor and its signal conditioning unit). 2, 0-10 V analog output signals are incorporated among which one is used to generate linear increasing filament voltage and other is used to control the control grid supply. 14 digital i/p channels (0 volts as logic 0 and 24 V as logic 1) are incorporated out of which 5 channels are digital i/p commands from remote namely system off, reset, B_H on, S_B on and Tx on. Other 6 channels are used for digital status signals of auxiliary electron gun supplies. One i/p is used for series combination of limit switches from flow signals of LCW water. One i/p is used for door interlock of HV deck and remaining one is used for air pressure switch. 4 digital o/p signals (logic level is same as digital i/p signals) are incorporated out of which 1 digital o/p is used to initiate the turn on operation i.e. heater I step on. Other one channel is used for Tx on and remaining 2 channels are used to interface with FM 352-5 for fast interlock processing in which one is HV ready signal and other is quiescent beam current status signal. Figure 6: Flow chart of operation of IOT amplifier system. Here all preconditions are necessarily included monitoring of coolants flow and temperature status. At any stage of operation cycle whenever any precondition is not satisfied control system detects the fault, latches it and takes the amplifier system to a predefined safe stage according to program of PLC. RESULTS AND CONCLUSION It is noteworthy that PLC operates in cyclic fashion where the one cycle execution time for slow interlock signal is found to be much less than 100 ms, while the time critical fast interlock execution time is found to be less than 10µs. These timing ranges are meeting the requirement regarding maximum allowed overload period of the IOT amplifier system. This system has been tested up to about 50 hrs satisfactorily with nil false tripping in the environment of indus-2 RF area. It saved a lot of wiring and maintenance efforts. So it is found suitable as control, interlock and monitoring system of 80 kW high power IOT amplifier system. [1] [2] REFERENCES http://www.e2v.com http://support.automation.siemens.com