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Digester Charging Control System
Copyright © IFAC Instrumentation and Automation in the Paper, Rubber, Plastics and Polymerization Industries, Ohio, USA, 1986
DIGESTER CHARGING CONTROL SYSTEM Sun Ao Research Institute for Automation & Instrumentation, Ministry of Light Industry, Hangzhou, PRG
Abstract. It is very difficult to control accurately the weight ratio of air-dried straw, alkali, and water in straw digester charging process. Because the volume weight of straw is very light, it can not be accurately weighed by the belt scale. In the southern part of China, the storage pile is much affected by the weather, the moisture of straw material may vary from 13% to 40%. The moisture of straw differs very much in the same storage pile. So the measurment of the sample moisture can not give the exact moisture content for the operator. Thus the operator can not charge the digester with the accurate alkali and liquor. We have developed a digital digester charging control system. The system can on-line synchronously measure the weight and moisture of straw. The total dieester chnrging weight and water weight can be instantaneously calculated by microcomputer. On this baSiS, system can accurately control the alkali and liquor, and the charging quality can be ensured. KeywordS. Control system synthesis; computer applications; microwave mOisture measurement; weight measurement using electronic belt scale; digester charging processing.
INTRODUCTION In the southern part of China, there are many paper and pulp mills where straw pulp is made by alkali methode. According to the technical schedule, the control of weight ratio among absolute dried straw, alkali and water is very important in digester charging process. Generally speaking, the old digester charg ing control methode is scaling total weight of straw bunches before sending them into the straw cutter, and measuring the mOisture of the straw sample which is often taken out from the the straw cutter. Usually the moisture of the sample is measured by drying methode. Then the total weight of water and alkali needed to be charged into the digester is calculated in the laboratory. The operator controls the digester charging weight of alkali and water in accordance with above
calculated data. The result obtained by this methode is not so good. Because straw piles are stored on the ground, the mOisture of the straw is much affected by weather. If the weather keeps fine in a long period, the straw pile is air dried, and its moisture tends to be an average among 13%-18%. But when it rains continuously, the values of the mOisture differ very much in the same straw pile, and some values may reach 30-40%. So the moisture of the straw materials may vary greatly during the digester charging process. While measuring moisture manualy, the straw sampled only three times in the digester charging process. The sample's quantity is too little to represent the exact moisture 123
Sun Ao
124
of all straw material. In this case, the calculated data of the total absolute dry straw weight, alkali weight and water weight is not reliable. Although operator accurately controls digester charging process according to the above calculated data, the effect of the digestion is not satisfied. On the other hand, the measuring period of the straw mOisture is too long. When data is obtained, the digester charging proce s s is nearly finished. Thus the measured information can not be used for realtime control. In finding some problems, We have tested fifty random probes of the fifty digesting processes, and each of the probes was operated in the same kind of straw materials, apparatus, and technical factors. The results show that the Kappa numbers of 10 probes are not qualified, qnd the 24 values of the remained alkali in the black lye are not qualified. Since all t he digestion processes a re operated under the same condition, we can take for granted that the non-qualified Kappa numbers and remained alkali values are caused by the non- reliable digester charging control. So that we designed a new digester charging control system, and improved the quality of the di gestion . SOME FUNDMENTAL IDEAS OF THE SYSTEM DESIGN The design of the new digester charging control system must solve two problems. 1. How can we obtain the accurate values of the absolute dry fiber weight and water weight of straw materials which are charged into digester?
2. How can we repidly and accurately calculate all data which are needed to the digester charging real time control? We developed three devices to solve these two problems . DEVICES
(1) Microwave moisture on-line measure meter WS-2 The WS-2 consists of five parts (see Fig.1) which are microwave Power detector, mois-
ture transducer, microwave generator, measure circuit and data processor. The microwave generator produces a steady microwave power which passes through waveguide and is recieved by the microwave power detector. The waveguide is a moisture transducer, on the top of which, a sensitive slot is excavated. The straw mat e rials are falling down from the el e ctronic belt sc ale, and passes across the sensitive slot. At this moment, the straw materials consume microwave power. The power consumption responds to the dielectric constant of the straw materials, which is the mixed dielectric constant of fiber and water. The stat ionary dielectric const ant of water is 78.5, and fiber is 3.3, so thedielectric constant of water i s the main part caus ing the consumption of microwave power, and the microwave powe r variation represent the straw mo i s ture variation. The measure circuit converts the variat ion of the microwave powe r into the variation of t he elec tric al signal. The data processor recieves analogical s ignal from measure circuit tlventy times per second and converts it into averaged digital value of moisture . On the front view of the data processor, a diRital indicator and a record printer have been set. Because the moisture transducer works in the very bad enVironment, some special arrangements ar e conSidered, e. g . dust protection, vibration protection, water protection, and abrasion protection, etc •• The moisture measure range of the WS-2 is 8-55%, and the stationary measure error is less than ;t1 %. (2) F.W. combination electronic belt scale DDC-1 Usually, in paper mills, straw bunches are hand-cart ed from store ground to the cutter. As straw passing through the weighhouse, the weigher records the total weight of straw bunches and the handcart with a ground scale, then he minuses the handcart 's weight from the total weight and obtains the straw bunches' weight. The merit of this methode is the increase in weighing
Digester Charging Control System
accuracy, because the volumetric weight of straw bunches is much larger than the volumetric weight of loose straw pieces. But this methode has some demerits. (a) In straw cutting operation, the consumption of straw is not calculated. (b) It is very difficult to measure moisture of straw bunches on-line. (c) The digester charging automatic control system can not be designed with the ground scale. So that some paper mills use the belt scale, but this is no success. Because the loose straw pieces is too light, and the sensitive quantity of the belt scale is very small, the measure error is very large and may reach 5-10%. We have developed a fiber and water combinative electronic belt scale DDC -1. Its construction is shown in Fig. 2. The DDC-1 consists of three parts: the electronic belt scale, the on-line moisture meter WS-2 and the data processor. The electronic belt scale possesses some special characters, e.g. the application of the strong elastic and uniform thickness belt, light and handy scale body, high accurate speed transducer and Weight transducer, etc •• An automatic scale zero point regulating circuit is also used in the measure block of t he scale, so that the zeropoint floating error is decreased, and the stationary error of the electronic belt scale is less than 0.1%. The microwave on-line moisture measure meter WS-2 is set on the out Side of the electronic belt scale. When the straw pieces pass through the electronic belt scale continually, the speed transducer and weight transducer immediately convert the straw piece weight and belt speed into electrical analogue signals. Then the straw pieces pass through the microwave moisture transducer which may convert moisture of straw pieces into the analogue signal. All of the signals are transmitted to the data processor.
where Wm----weight of water in straw pieces Ws----weight of straw pieces Waf---weight of absolute dry fiber Ms----moisture of straw pieces the data processor calculates Wm, Waf. But there is a short distance between the electronic belt scale's transducer and the microwave moisture transducer, so it will cause a time difference which may produce calculative errors on Wm and Waf. By mathematical analySiS, this error is very little in general cases, and we may neglect it. But if the materials are badly distributed into the F.W. combinative electronic belt scale, and the time of the whole digester charging process is very short, this error will increase, so that we have synchoronized the two signals with the processor. The data processor's main function is described below. (a) Total s t raw weight display and print, (b) Straw moisture display and print, (c) Absolute dry fiber weight display and print, (d) Weight extending alarm, (e) Zeropoint automatic regulation, (f) Self-breakdown alarm. The weighing range of the F.W. combinative electronic belt scale is 12T/hr. (3) Microcomputer-based digester charging controller PK-l The main requests of the digester charging control system to a controller are as follows. 1. Automatic monitor of the whole working procedure of the digester charging process. 2. Proportional control of absolute dry fiber weight, alkali weight, and water Weight.
3. Display and record of the conSidered data.
According to the formula 4. Preset of the operation data. Wm = Ws * Ms Waf= Ws - Wm
125
5. Self-detection of the control devices and alarm.
Sun Aa
126
The proportional control of digester charging materials can be operated in two ways. The first way is charging straw, alkali and water according to their preset values, and ensuring the weight proportion at the end of the charging process. The second way is using a random proportional control system which may keep the preset value ratio among fiber, alkali and water at any time during the charging process. Both of the two ways can be designed as open-l oop system or close-loop system, which depends on the control accuracy. Accordi ng to above requirements, we have designed the PK-1, and its front panel arrangement is shown in Fig . 3. The PK-1 is designed in the first way. It controls a digester charging line. According to the preset values, PK-1 controls the charging weight of the absolute dry fiber, and then instantaneously controls the flow of alkali liquor in open-circuit form. At the end of the process, PK-1 calculates the weight of replenished water Wr by the formula Wr
= Wt
fixed cocentration is filled in a measure vessel, and the liquid l evel of the vessel indicates the volume of the alkali liquor. When the digester charging process begins, the straw pieces continually pass through the F.W. combinative electronic belt scale, and the scale converts the weight and the mOisture of the straw pieces into electrical signals instantaneously.The processore~ of the WS-2 and DDC-1 accept these Signals and calculate the total weight of straw pieces , absolute dry fiber, and water in straw pieces. Then the microcomputer-based dig ester charging controller PK-1 calcul ate the weight of the replenished water. At this moment, PK-1 proportionally controls the regulating valve of the alkali liquor and keeps the weight ratiO between the absolute dry fib er and alkali to a constant When the absolute dry fiber weight tends to the preset value, PK-1 will stop the digester charging operation, and display the replenished wat er weight . Then the operator replenishes the water with regard to the displayed value. When the weight of alkali also tends t o the pres et value , the regulating valve of alkali liquor is fully closed.
- Wl - Ws
whereWt----total water needed in digestion Wl----total water component of the alkali liquor Ws----total water consisted in the straw materials and display the digital value of the Wr. The printer of the PK-1 can print daily operation data table . The PK-1 is constructed on the STD model units, so that it is very easy to develop its control action.
SYSTEM (1) Preset weight digester charging control system The simple structure of the system is shown in Fig. 4. The charging weight of the absolute dry fiber is previously set by the technical stipulation, so the total weights of alkali and water can also be previously calculated. The alkali liquor which has the
This system is very easy to adopt . It is not necessary for paper mills to change the original equipment. But the system will loss productivity to some extent and can not be used i n continuous dig esting process. (2) Random proportional digester charging control system In the digester charging process, there are some variations in the volumetric weight of straw pieces, and the digester charging operation is different, so the charging weight of straw pieces may also be very different. For example, a digester's normal charging weight is 7000kg, but sometimes its practical charging weight may extend to 8500kg. In general, operators want to increase productivity, so that they would increase the charging weight, but the preset weight digester charging control system can not be content with this good will. The random proportional dig ester charging
127
Digester Charging Control System
control system is based on the development of PK-1. This system can instantaneously and proportionally control the replenished water and alkali liquor according to the calculated weight of the absolute dry fiber, and transport the mixture into the diges ter. When the digester is fully filled. PK-1 will stop the charging process immediat ely. This system can increase the productivity with the same di gester, and control continuous digester charging process. The charging materials is fully mixed and accurately, proport ionally cont roled, so the quality requirements of the digesting process can be satisfied.
CONCLUSION We developed three successful deVices, e.g.
on-line microwave moisture measure meter WS-2, electronic straw pieces belt scale DDC-1, and microcomputer-based proportional digester charging controller. These devi ces open up a broad prospect for digester charging control system designers. Every device can also be used together or individually in other industrial control system. The preset weight digester charging control system suits the improvement of t he old paper mills in the developing country, because the old paper mills are very difficult to change original eqUipment for a new control system. The random proportional digester charging control system suits the new mill deSign, because the new mill permits to build new machines for the continuous supply of the alkali liquor and water.
..
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~ 1. 2. 3. 4. 5. 6.
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Fig. 1 Moisture indicator and printer Datalog Moisture transducer Straw material Microwave generator and power detector Measure circuit
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Fig. 2 1.Set weight finish signal 2 .Zero ~gula tion Signal 3. Overload alarm 4.Absolute dry weight print 5.Total absolute dry weight print 6.Total weight print 7.Weight indicator 8.Total weight indicator 9.Belt speedtransducer 10.Weight transducer 11.Moisture transducer 12.Belt scale 13. Straw material 14. Data logical device DDC-1
128
Sun Aa
Fig. 3.
PK-1 controller 6. MOisture defect sie nal 7. Key board
1. Printer 2. ON-OFF breaker
3. Sour ce signal 4. Monitor signal 5. Air- dried straw weight indicator
8 . Electronic bel t scale overload , noload and defect signal
9. Preset weig ht signal 10 . Repair \{at e r weight indi cator
..
St r aw ma terial
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--,
--,
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DDC-1
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PK-1
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DIGESTER CHARGING CONTROL SYSTEM Sun Ao Research Institute for Automation & Instrumentation, Ministry of Light Industry, Hangzhou, PRG
Abstract. It is very difficult to control accurately the weight ratio of air-dried straw, alkali, and water in straw digester charging process. Because the volume weight of straw is very light, it can not be accurately weighed by the belt scale. In the southern part of China, the storage pile is much affected by the weather, the moisture of straw material may vary from 13% to 40%. The moisture of straw differs very much in the same storage pile. So the measurment of the sample moisture can not give the exact moisture content for the operator. Thus the operator can not charge the digester with the accurate alkali and liquor. We have developed a digital digester charging control system. The system can on-line synchronously measure the weight and moisture of straw. The total dieester chnrging weight and water weight can be instantaneously calculated by microcomputer. On this baSiS, system can accurately control the alkali and liquor, and the charging quality can be ensured. KeywordS. Control system synthesis; computer applications; microwave mOisture measurement; weight measurement using electronic belt scale; digester charging processing.
INTRODUCTION In the southern part of China, there are many paper and pulp mills where straw pulp is made by alkali methode. According to the technical schedule, the control of weight ratio among absolute dried straw, alkali and water is very important in digester charging process. Generally speaking, the old digester charg ing control methode is scaling total weight of straw bunches before sending them into the straw cutter, and measuring the mOisture of the straw sample which is often taken out from the the straw cutter. Usually the moisture of the sample is measured by drying methode. Then the total weight of water and alkali needed to be charged into the digester is calculated in the laboratory. The operator controls the digester charging weight of alkali and water in accordance with above
calculated data. The result obtained by this methode is not so good. Because straw piles are stored on the ground, the mOisture of the straw is much affected by weather. If the weather keeps fine in a long period, the straw pile is air dried, and its moisture tends to be an average among 13%-18%. But when it rains continuously, the values of the mOisture differ very much in the same straw pile, and some values may reach 30-40%. So the moisture of the straw materials may vary greatly during the digester charging process. While measuring moisture manualy, the straw sampled only three times in the digester charging process. The sample's quantity is too little to represent the exact moisture 123
Sun Ao
124
of all straw material. In this case, the calculated data of the total absolute dry straw weight, alkali weight and water weight is not reliable. Although operator accurately controls digester charging process according to the above calculated data, the effect of the digestion is not satisfied. On the other hand, the measuring period of the straw mOisture is too long. When data is obtained, the digester charging proce s s is nearly finished. Thus the measured information can not be used for realtime control. In finding some problems, We have tested fifty random probes of the fifty digesting processes, and each of the probes was operated in the same kind of straw materials, apparatus, and technical factors. The results show that the Kappa numbers of 10 probes are not qualified, qnd the 24 values of the remained alkali in the black lye are not qualified. Since all t he digestion processes a re operated under the same condition, we can take for granted that the non-qualified Kappa numbers and remained alkali values are caused by the non- reliable digester charging control. So that we designed a new digester charging control system, and improved the quality of the di gestion . SOME FUNDMENTAL IDEAS OF THE SYSTEM DESIGN The design of the new digester charging control system must solve two problems. 1. How can we obtain the accurate values of the absolute dry fiber weight and water weight of straw materials which are charged into digester?
2. How can we repidly and accurately calculate all data which are needed to the digester charging real time control? We developed three devices to solve these two problems . DEVICES
(1) Microwave moisture on-line measure meter WS-2 The WS-2 consists of five parts (see Fig.1) which are microwave Power detector, mois-
ture transducer, microwave generator, measure circuit and data processor. The microwave generator produces a steady microwave power which passes through waveguide and is recieved by the microwave power detector. The waveguide is a moisture transducer, on the top of which, a sensitive slot is excavated. The straw mat e rials are falling down from the el e ctronic belt sc ale, and passes across the sensitive slot. At this moment, the straw materials consume microwave power. The power consumption responds to the dielectric constant of the straw materials, which is the mixed dielectric constant of fiber and water. The stat ionary dielectric const ant of water is 78.5, and fiber is 3.3, so thedielectric constant of water i s the main part caus ing the consumption of microwave power, and the microwave powe r variation represent the straw mo i s ture variation. The measure circuit converts the variat ion of the microwave powe r into the variation of t he elec tric al signal. The data processor recieves analogical s ignal from measure circuit tlventy times per second and converts it into averaged digital value of moisture . On the front view of the data processor, a diRital indicator and a record printer have been set. Because the moisture transducer works in the very bad enVironment, some special arrangements ar e conSidered, e. g . dust protection, vibration protection, water protection, and abrasion protection, etc •• The moisture measure range of the WS-2 is 8-55%, and the stationary measure error is less than ;t1 %. (2) F.W. combination electronic belt scale DDC-1 Usually, in paper mills, straw bunches are hand-cart ed from store ground to the cutter. As straw passing through the weighhouse, the weigher records the total weight of straw bunches and the handcart with a ground scale, then he minuses the handcart 's weight from the total weight and obtains the straw bunches' weight. The merit of this methode is the increase in weighing
Digester Charging Control System
accuracy, because the volumetric weight of straw bunches is much larger than the volumetric weight of loose straw pieces. But this methode has some demerits. (a) In straw cutting operation, the consumption of straw is not calculated. (b) It is very difficult to measure moisture of straw bunches on-line. (c) The digester charging automatic control system can not be designed with the ground scale. So that some paper mills use the belt scale, but this is no success. Because the loose straw pieces is too light, and the sensitive quantity of the belt scale is very small, the measure error is very large and may reach 5-10%. We have developed a fiber and water combinative electronic belt scale DDC -1. Its construction is shown in Fig. 2. The DDC-1 consists of three parts: the electronic belt scale, the on-line moisture meter WS-2 and the data processor. The electronic belt scale possesses some special characters, e.g. the application of the strong elastic and uniform thickness belt, light and handy scale body, high accurate speed transducer and Weight transducer, etc •• An automatic scale zero point regulating circuit is also used in the measure block of t he scale, so that the zeropoint floating error is decreased, and the stationary error of the electronic belt scale is less than 0.1%. The microwave on-line moisture measure meter WS-2 is set on the out Side of the electronic belt scale. When the straw pieces pass through the electronic belt scale continually, the speed transducer and weight transducer immediately convert the straw piece weight and belt speed into electrical analogue signals. Then the straw pieces pass through the microwave moisture transducer which may convert moisture of straw pieces into the analogue signal. All of the signals are transmitted to the data processor.
where Wm----weight of water in straw pieces Ws----weight of straw pieces Waf---weight of absolute dry fiber Ms----moisture of straw pieces the data processor calculates Wm, Waf. But there is a short distance between the electronic belt scale's transducer and the microwave moisture transducer, so it will cause a time difference which may produce calculative errors on Wm and Waf. By mathematical analySiS, this error is very little in general cases, and we may neglect it. But if the materials are badly distributed into the F.W. combinative electronic belt scale, and the time of the whole digester charging process is very short, this error will increase, so that we have synchoronized the two signals with the processor. The data processor's main function is described below. (a) Total s t raw weight display and print, (b) Straw moisture display and print, (c) Absolute dry fiber weight display and print, (d) Weight extending alarm, (e) Zeropoint automatic regulation, (f) Self-breakdown alarm. The weighing range of the F.W. combinative electronic belt scale is 12T/hr. (3) Microcomputer-based digester charging controller PK-l The main requests of the digester charging control system to a controller are as follows. 1. Automatic monitor of the whole working procedure of the digester charging process. 2. Proportional control of absolute dry fiber weight, alkali weight, and water Weight.
3. Display and record of the conSidered data.
According to the formula 4. Preset of the operation data. Wm = Ws * Ms Waf= Ws - Wm
125
5. Self-detection of the control devices and alarm.
Sun Aa
126
The proportional control of digester charging materials can be operated in two ways. The first way is charging straw, alkali and water according to their preset values, and ensuring the weight proportion at the end of the charging process. The second way is using a random proportional control system which may keep the preset value ratio among fiber, alkali and water at any time during the charging process. Both of the two ways can be designed as open-l oop system or close-loop system, which depends on the control accuracy. Accordi ng to above requirements, we have designed the PK-1, and its front panel arrangement is shown in Fig . 3. The PK-1 is designed in the first way. It controls a digester charging line. According to the preset values, PK-1 controls the charging weight of the absolute dry fiber, and then instantaneously controls the flow of alkali liquor in open-circuit form. At the end of the process, PK-1 calculates the weight of replenished water Wr by the formula Wr
= Wt
fixed cocentration is filled in a measure vessel, and the liquid l evel of the vessel indicates the volume of the alkali liquor. When the digester charging process begins, the straw pieces continually pass through the F.W. combinative electronic belt scale, and the scale converts the weight and the mOisture of the straw pieces into electrical signals instantaneously.The processore~ of the WS-2 and DDC-1 accept these Signals and calculate the total weight of straw pieces , absolute dry fiber, and water in straw pieces. Then the microcomputer-based dig ester charging controller PK-1 calcul ate the weight of the replenished water. At this moment, PK-1 proportionally controls the regulating valve of the alkali liquor and keeps the weight ratiO between the absolute dry fib er and alkali to a constant When the absolute dry fiber weight tends to the preset value, PK-1 will stop the digester charging operation, and display the replenished wat er weight . Then the operator replenishes the water with regard to the displayed value. When the weight of alkali also tends t o the pres et value , the regulating valve of alkali liquor is fully closed.
- Wl - Ws
whereWt----total water needed in digestion Wl----total water component of the alkali liquor Ws----total water consisted in the straw materials and display the digital value of the Wr. The printer of the PK-1 can print daily operation data table . The PK-1 is constructed on the STD model units, so that it is very easy to develop its control action.
SYSTEM (1) Preset weight digester charging control system The simple structure of the system is shown in Fig. 4. The charging weight of the absolute dry fiber is previously set by the technical stipulation, so the total weights of alkali and water can also be previously calculated. The alkali liquor which has the
This system is very easy to adopt . It is not necessary for paper mills to change the original equipment. But the system will loss productivity to some extent and can not be used i n continuous dig esting process. (2) Random proportional digester charging control system In the digester charging process, there are some variations in the volumetric weight of straw pieces, and the digester charging operation is different, so the charging weight of straw pieces may also be very different. For example, a digester's normal charging weight is 7000kg, but sometimes its practical charging weight may extend to 8500kg. In general, operators want to increase productivity, so that they would increase the charging weight, but the preset weight digester charging control system can not be content with this good will. The random proportional dig ester charging
127
Digester Charging Control System
control system is based on the development of PK-1. This system can instantaneously and proportionally control the replenished water and alkali liquor according to the calculated weight of the absolute dry fiber, and transport the mixture into the diges ter. When the digester is fully filled. PK-1 will stop the charging process immediat ely. This system can increase the productivity with the same di gester, and control continuous digester charging process. The charging materials is fully mixed and accurately, proport ionally cont roled, so the quality requirements of the digesting process can be satisfied.
CONCLUSION We developed three successful deVices, e.g.
on-line microwave moisture measure meter WS-2, electronic straw pieces belt scale DDC-1, and microcomputer-based proportional digester charging controller. These devi ces open up a broad prospect for digester charging control system designers. Every device can also be used together or individually in other industrial control system. The preset weight digester charging control system suits the improvement of t he old paper mills in the developing country, because the old paper mills are very difficult to change original eqUipment for a new control system. The random proportional digester charging control system suits the new mill deSign, because the new mill permits to build new machines for the continuous supply of the alkali liquor and water.
..
r-
6
~ 1. 2. 3. 4. 5. 6.
I I I
,
I I I1 I1 II
!I
1
7(
2
Fig. 1 Moisture indicator and printer Datalog Moisture transducer Straw material Microwave generator and power detector Measure circuit
I
13
/2.
,---
/0
I I I I
L
-
a
-
6 5
7
I 1---
14
4-
3 2I
Fig. 2 1.Set weight finish signal 2 .Zero ~gula tion Signal 3. Overload alarm 4.Absolute dry weight print 5.Total absolute dry weight print 6.Total weight print 7.Weight indicator 8.Total weight indicator 9.Belt speedtransducer 10.Weight transducer 11.Moisture transducer 12.Belt scale 13. Straw material 14. Data logical device DDC-1
128
Sun Aa
Fig. 3.
PK-1 controller 6. MOisture defect sie nal 7. Key board
1. Printer 2. ON-OFF breaker
3. Sour ce signal 4. Monitor signal 5. Air- dried straw weight indicator
8 . Electronic bel t scale overload , noload and defect signal
9. Preset weig ht signal 10 . Repair \{at e r weight indi cator
..
St r aw ma terial
Ci
~
k~
-
--,
--,
I
I
I
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DDC-1
I
L __
,--
PK-1
I
I
II
IL ________________ ~ I I
I I
L ___________ - _____ _ Fig. 4