Application of the hottest wf705 in RH vacuum trea

Application of wf705 in RH vacuum treatment control system

Panzhihua Iron and Steel Co. built a RH vacuum treatment device with an annual treatment capacity of 500000 tons of molten steel in early 1998. Its main functions are: dehydrogenation, deoxidation, decarburization and alloying of molten steel from the converter. After RH vacuum treatment, the properties of molten steel have been greatly improved, which can improve the product quality of cold-rolled sheet at Pangang

1 composition of the control system

Siemens suplc is used in the RH vacuum treatment basic automatic control system of Panzhihua Iron and Steel Co., Ltd. the whole control system is composed of plc1, plc2, oms1, oms2, level2 (secondary computer) and pg760. The system is connected into a whole through sinech1. Plc1 controls the vacuum treatment part and plc2 controls the alloy feeding part. Oms1 and oms2 are operation stations. Level2 calculates the amount of alloy to be added through a certain mathematical model according to the composition and physical state of molten steel during vacuum treatment, and sends control instructions to the basic automation level (PLC). Pg760 is an engineer station, which is used to program and monitor the operation of programs

MFB (multi function burner) gun is a very important equipment in RH vacuum treatment. Its function is to heat the vacuum chamber by atmospheric heating in the non treated state; Vacuum heating is carried out in the treatment process to reduce the temperature drop of molten steel; Blowing oxygen into molten steel for forced decarburization; The molten steel is heated by injecting oxygen and adding aluminum shot for chemical heating. To achieve the above functions, the MFB gun must be accurately positioned. This paper introduces how to use absolute encoder, Siemens wf705 position module and PLC to realize the accurate positioning of MFB gun

2 hardware configuration

the absolute encoder is installed on the motor shaft driving the MFB gun and rotates with the rotation of the motor. The encoder sends 1024 pulses every revolution. Wf705 receives the pulse signal sent by the encoder and accumulates the pulse value, and then sends it to PLC to calculate the actual position of MFB gun

the system adopts the multi － turnssiawc5810 absolute encoder of fraba company in Germany, and its maximum counting capacity is 1024 × 16 = 16384 pulses, which adopts gray code 25bit data format. According to the different cable length, the data transmission rate has 125k, some of which are caused by the machine itself, b/s (120m) and 1mb/s (25m)

wf705 is actually equivalent to a position decoder, which is directly inserted into the PLC rack. The absolute encoder is connected to the synchronous serial interface of wf705 through 7-core shielded cable, and its 24VDC power supply is provided by wf705. Wf705 must set an address (set by the address switch on the module) so that the CPU can address it. The address of wf705 in this system is set to 240

3 software design

3.1 program structure

plc program is compiled with step5 language, and the program structure is block structure. The program related to wf705 only needs to call the relevant S5 standard function block in the step5 application program of PLC. S5 standard function block is provided with step5 software

the function blocks related to wf705 are fb160, fb161 and fb163. Fb160 and fb163 are used for the synchronization of CPU and wf705 when PLC is started. They are called and executed only once by ob20/ob21/ob22 when PLC is started. Wf705 is initialized, and fb163 is called in fb160, which automatically generates a 48 word data block for storing the actual pulse value transmitted by wf705. Fb161 is used to read the pulse value in wf705 to the CPU. It is called and executed circularly in ob1, and the pulse value of the encoder is accumulated in real time

in this control system, in order to make the program more concise and readable, fb160 is programmed in Pb2, and then ob20/ob21/ob22 calls PB2 to initialize wf705. Program fb161 into PB3, and then ob1 calls PB3 to read the pulse value from wf705 to CPU. In this way, the structure of the program is clearer

3.2 parameter configuration of function block

when programming, you can directly call fb160, fb161, fb163, but you must also configure their parameters. Because fb163 is an internal call, there is no need to configure the parameters of fb163

fb160 is as follows:

(1) data block DB12 storing pulse values

(2) pulse number of absolute encoder per cycle 1024

(3) module address 240 of wf705

(4) data transmission rate 125kb/s

the parameter configuration of fb161 is as follows:

(1) data block DB12 storing pulse values

(2) synchronous serial interface (SSI) number 2

3.3 value conversion of wf705.

since the CPU reads only the pulse value from fb161, To express the growth unit mm, it must also be converted. The conversion formula is as follows:

where D is the actual displacement; P is the actual pulse value; L is the maximum stroke; R is the number of turns that the encoder turns in the whole stroke

the maximum stroke L is the distance between the upper/lower limits of the MFB gun, which is measured manually with a tape measure; The number of turns r of the encoder is calculated by the following relationship: r= (pup pdown)/1024, where pup is the number of pulses when the MFB gun is at the upper limit, and pdown is the number of pulses when the MFB gun is at the lower limit. This conversion function is realized by self-made function block fb232

3.4mfb gun positioning control

as mentioned above, MFB gun has four functions. When realizing these four functions, the positions of MF and B gun are different: (1) atmospheric heating gun position is 5.0 ~ 7.0m; (2) Vacuum heating gun position 5.5 ~ 7.0m; (3) With the concept and development mode of "Internet +", chemplus is deeply rooted in the hearts of the people. The hot gun level is 2.5 ~ 5.0m; (4) The forced decarbonization gun position is 2.0 ~ 5.0m

mfb gun's gun position setting has two ways to measure the force required to expand the tear: the first is computer (level2) mode, which is requested manually, and the computer calculates according to the mathematical model, gives the gun position setting value under various conditions, and sends it to PLC; The second is manual mode. The operator inputs the set value of MFB gun position under various conditions on the operation station and sends it to PLC through H1

plc receives the set value of MFB gun, compares it with the actual gun position, and then sends instructions to control the rise and fall of MFB gun. MFB gun has two operating speeds: fast and slow. When MFB gun acts, it always runs quickly first. When the actual gun position is different from the set value Δ When l ≤± 100mm, turn to low-speed operation, when Δ When l ≤± 10mm, the MFB gun stops running and stops at the set position after sliding for a certain distance due to inertia. The deviation of ± 10mm is determined according to the actual situation on site during commissioning