The choice measure of PLC type and capacity and principle

The development of the choice measure of PLC type and principle as PLC technology, the sort of PLC product is increasing also. The PLC of different type, means of system of its configuration, function, capacity, instruction, process designing, price also have each different, applicable circumstance also has each emphasize particularly on. Accordingly, reasonable choose PLC, the technical economic norms that controls a system to raising PLC is having important sense. The alternative of PLC is main should the respect such as ability of net of couplet of module of the type from PLC, capacity, I/O, power source module, special function module, communication tries to consider integratedly. The chooses PLC type option basic principle of PLC type is to satisfying a function to ask to reach assure reliable, safeguard convenient premise to fall, strive first-rate performance/price ratio. The following basically considers when the choice: (One) reasonable structural type PLC basically has integral type and module type type of two kinds of structures. The average price that the O of each I ／ of integral type PLC selects compares the petty gain of module type, and volume is relatively minor, use at systematic process commonly in relatively fixed small-sized control system; And the function of module type PLC is patulous and agile convenient, the respect such as the sort of module of O of ／ of the scale in check the number of I ／ O, input check the number and output check the number, I chooses leeway big, and maintenance is convenient, general at more complex control system. (2) the installation means cent of the choice PLC system that installs means is concentration of type of type, O of long-range I ／ and net of couplet of much stage PLC distributed. Collect Chinese style does not need to install drive hardware of O of long-range I ／ , the system reacts fast, cost is low; Type of O of long-range I ／ applies to large system, systematic unit is distributed range is very wide, OK and dispersive installation is in O of long-range I ／ near site plant, connect line weak point, but need adds driver and power source of O of long-range I ／ ; Of net of couplet of much stage PLC distributed apply to much stage equipment to be controlled independently respectively, want the circumstance of mutual connection again, can choose small-sized PLC, but must want add communication module. (3) corresponding functional requirement is general and small-sized (cheap) PLC has the function such as logistic operation, time, computation, to needing switch to measure pilot only equipment can be satisfied. Give priority to to measuring control with switch, take a few imitate to measure pilot system, can choose can take A ／ D and D ／ A to change unit, have add those who decrease arithmetic manipulation, number to send a function as it is said to increase model cheap PLC. More complex to control, the requirement realizes the function such as net of couplet of PID operation, closed-loop control, communication, can inspect control scope magnitude and complex degree, choose intermediate or high-grade PLC. But price of medium, high-grade PLC is more expensive, use at the circumstance such as extensive process control and system of distributing center control commonly. (4) the current controller that answers speed to ask PLC is to be industrial automation to design, the response of different class PLC speed can satisfy his to apply the need inside limits commonly. If want to cross limits to use PLC, when certain perhaps function or signal have special rate to ask, should consider PLC cautiously answer speed, optional appliance has O of ／ of high speed I to handle functional PLC, or choose appliance to have answer module and the PLC that interrupt input module to wait quickly. (5) the requirement of systematic dependability all can be satisfied to the dependability of average system PLC. Very expensive to dependability requirement system, whether Lv of take an examination uses redundant system or heat reserves system. (6) type consolidates an industry as far as possible, the type that should accomplish PLC as far as possible is unified. Basically consider issue of side of the following tripartite: １ ) type is unified, its module but each other is reserve, facilitating machine parts or tools kept in reserve spares parts purchase and manage. 2) type is unified, its function and use method is similar, be helpful for technical force groom and of technical level rise. 3) type is unified, its peripheral equipment is current, resource can be shared, easily couplet net corresponds, deserve to go up a multistage is formed easily after the computer distributed control system. The chooses measure and principle </DIV><DIV></DIV><DIV>PLC capacity of <DIV Id=Title>PLC capacity includes check the number of I ／ O and user memory capacity two respects. (One) the price that the I ／ O with the choice average PLC of check the number of I ／ O selects is higher, the quantity that because this should be reasonable,the I ／ O that chooses PLC orders, the dot of I ／ O that strives to use below the premise that asks in contented control is least, but must take the abundant amount with have certain. Normally check the number of I ／ O is a basis the input of object be accusinged, real need that outputs signal, plus the abundant of ％ of 10 ％ ~15 the capacity decides. (2) the memory capacity size that the place of choice user program of memory capacity wants is concerned with the function of PLC system not only, and the method that still implements with the function, program writes a level to concern. One has the programmer of experience and an abecedarian, when fulfilling same and complex function, its program volume may differ of 25 ％ , should take abundant amount more when memory capacity estimation to abecedarian so. How many of the check the number of I ／ O of PLC, the functional demand of PLC system was reflected on very large order, because this can be on the foundation with certain check the number of I ／ O, press after type estimation memory capacity, increase the abundant amount of ％ of 20 ％ ~30 again. Memory capacity (byte) passageway of O of ／ of I of quantity of imitate of ＋ of 10 of × of check the number of O of ／ of I of ＝ switch quantity counts × 100 additional, while memory capacity chooses, note the alternative of the type to memory. </DIV> CNC Milling