Using the HT45R38 to Measure Current and Voltage and Power Adjustment for Electric Hotplates

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1 Using the HT45R38 to Measure Current and Voltage and Power Adjustment for Electric Hotplates D/N: HA0146E Introduction In past years Electric Hotplates have become a common household electrical appliance possessing the following advantages: no flame, no smoke, power savings, time savings, ease of use etc. Electric hotplates have developed from the original hardware control to the present MCU control. The Holtek A/D type MCUs have seen extensive use in these applications and offer the advantages of low cost, high efficiency and rapid development times etc. The MCUs used in Electric Hotplates are: HT46R47, HT46R22/HT46R23, HT46R12A/ HT46R14A, HT46R32/HT46R34/HT46R322/HT46R342, HT45R38 etc. This application introduces an Electric Hotplate current measurement method and voltage measurement method. The main reason for measuring voltage and current is to calculate the power level, and if compared with the setup values of power, the result can be used to adjust the PWM level to achieve a stable power objective. 1

2 Current Measurement Principles IGBT Heating coil base Internal HT45R38 OPA HT45R38 MCU ADC0 input IGBT drive circuit Constantan Current Measurement Description Because electric hotplates operate using an electric heating a heating coil, there must be some method to measure the heating coil current. The method of detecting the current is to insert a 0.01Ω/3W constantan resistor in the ground circuit of the IGBT to enable conversion from current to voltage. This voltage can then by amplified by the internal op-amp in the HT45R38 and then given to the A/D channel 1 for sampling. In the actual application, because the electric hotplate heating coil generates interference, therefore after sampling the signal a dual RC filter circuit is added. After the current signal is amplified, there is another RC filter and finally the ADC conversion. During the current sampling, the gain of the non-inverting amplifier circuit is given by (1+R7/R6)=1+100/10=1+10= 11 times. Current Sampling Software Handling Routine The important point of the current sampling software design is to manage the interference. The sampling of a signal within a certain range is known as software filtering. When 10 sample groups are effective, then the largest and the smallest are discarded and the two middle groups are taken, after which the average value found of these two groups. This average value is then taken as the first effective sampled value. The actual handling software is as follows: 2

3 The following is: sample 10 groups of effective current values. ; current_ad() CURRENT_AD: MOV A, ADRH ; ADRH is the AD conversion register MOV tmp_1, A ; temporary AD sample value SUB A, MIN_CURRENT ; MIN_CURRENT is minimum current value JMP CA_BLWMIN MOV A, MAX_CURRENT ; MAX_CURRENT is maximum current value SUB A, tmp_1 JMP CA_BLWMIN ; if the A/D sampled value is between the largest and smallest values, then handle ; as an effective value, otherwise handle as a signal with interference MOV A, ad_current_count ; ad_current_count is the sample value counter ADD A, OFFSET ad_current_buff ; ad_current_buff is the sample value RAM address MOV A, ADRH MOV R0, A INC ad_current_count ; after saving eff. current value increment sample ; counter CA_BLWMIN: MOV A, 9 ; determine if 10 eff. groups have been sampled SUB A, ad_current_count SZ C JMP EXIT_CURRENT_AD CLR ad_current_count ; 10 eff. group samples, clear sample counter EXIT_CURRENT_AD: ; end of current_ad()

4 The following software takes 10 groups of effective current values and after ordering, calculates the average of the two middle groups and then places this average value in the ad_work_current register. ; mean_current() ; Function description: ; Obtain mean current AD value ; from ad_current_buff with 10 values ; by using buble sort way. ; Input Parameter: ; ad_current_buff ; Output Parameter: ; ad_work_current MEAN_CURRENT: CLR loop_k ; loop_k used to indicate which loop JMP CURR_CHECK_LOOP_K CURR_NEXT_LOOP_K: CLR flag_sort_over CLR loop_n JMP CURR_CHECK_LOOP_N CURR_NEXT_LOOP_N: MOV A, loop_n ADD A, OFFSET ad_current_buff MOV tmp_1, A ; flag to indicate which sort has data for interchange ; from loop_n take the i data from the non order list ; take the i data from the non order list and store in tmp_1 INCA loop_n ADD A, OFFSET ad_current_buff ; from loop_n take the i+1 data from the non order list SUB A, tmp_1 ; compare the i+1 data and the i data SZ C JMP CURR_NOT_SWAP MOV A, loop_n MOV tmp_2, A ADD A, OFFSET ad_current_buff MOV tmp_3, A ; temporary data pointer INCA tmp_2 ADD A, OFFSET ad_current_buff 4

5 MOV tmp_2, A MOV A, tmp_3 MOV A, tmp_2 MOV R0, A INCA loop_n ADD A, OFFSET ad_current_buff MOV A, tmp_1 MOV R0, A SET flag_sort_over CURR_NOT_SWAP: INC loop_n CURR_CHECK_LOOP_N: MOV A, 9 SUB A, loop_k MOV tmp_2, A MOV A, loop_n SUB A, tmp_2 JMP CURR_NEXT_LOOP_N SNZ flag_sort_over JMP EXIT_CURR_MEAN INC loop_k ; the i+1 sort CURR_CHECK_LOOP_K: MOV A, loop_k SUB A, 9 JMP CURR_NEXT_LOOP_K ; take the i+1 data and store in tmp_2 ; take the i+1 data and store in the i data location ; place the i data value into the i+1 data location ; setup the data exchange flag ; increment loop_n value, compare the i+1 and i+2 data ; loop_k used to indicate the i loop ; loop_n indicates the i loop, data compare count ; not finished ; if no data exchange then end ; the i sort becomes the last, increment loop_k, execute ; when loop_k=9 all data sorts are finished EXIT_CURR_MEAN: MOV A, OFFSET ad_current_buff ; average value for centre two groups ADD A, 4 MOV tmp_1, A ; store the 5 group value in tmp_1 MOV A, OFFSET ad_current_buff 5

6 ADD A, 5 ; store the 6 group in A CLR C ADDM A, tmp_1 ; add the 5 and the 6 group values RRCA tmp_1 MOV ad_work_current, A ; finally store the current value in ad_work_current ; end of mean_current() Voltage Measurement Principle Power Line AC220V Rectifier Diodes Divider Network Filter Circuit Voltage Measurement Description The voltage measurement description circuit measures the voltage between the L and N lines. After rectification by D1 and D2, and division by resistor divider R1 and R2, filtering by C1 and additional filtering by R3 and C2, the signal is transmitted to channel AN3 of the HT45R38 for A/D conversion. In the diagram V0 is: 220V 1.414=311V and V1 is: 6.8K/(6.8K+560K) 311V=3.73V. Voltage Sampling Software Management Program The important point of the voltage sampling software design is to manage the interference. The sampling of a signal within a certain range is known as software filtering. When 10 sample groups are effective, then the largest and the smallest are discarded and the two middle groups are taken, after which the average value found of these two groups. This average value is then taken as the first effective sampled value. The actual handling software is as follows: 6

7 ; voltage_ad() VOLTAGE_AD: MOV A, ADRH ; ADRH is the AD conversion register MOV tmp_1, A ; temporary AD sample value SUB A, MIN_VOLTAGE-10 ; MIN_VOLTAGE-10 smallest voltage JMP VA_BLW10 MOV A, MAX_VOLTAGE+10 ; MIN_VOLTAGE+10 largest voltage SUB A, tmp_1 JMP VA_BLW10 ; if the A/D sampled value is between the smallest and largest value, then treat as an effective ; value, otherwise treat as a interference signal ; MOV A, ad_voltage_count ; ad_voltage_coun is he sample value counter ADD A, OFFSET ad_voltage_buff ; ad_voltage_buff is the sample value store address MOV A, ADRH MOV R0, A INC ad_voltage_count ; after storing eff. current value, increment sample couter VA_BLW10: MOV A, 9 ; determine if sampled 10 groups are eff. values SUB A, ad_voltage_count SZ C JMP EXIT_VOLTAGE_AD CLR ad_voltage_count ; already sampled 10 eff. value groups, clear counter EXIT_VOLTAGE_AD: ; end of voltage_ad() The following program sorts the 10 groups of effective voltage values. The average of the middle two groups is calculated and stored in ad_work_voltage. ; mean_voltage() ; Function description: ; Obtain mean voltage AD value ; from ad_voltage_buff with 10 values ; by using buble sort way. ; Input Parameter: ; ad_voltage_buff ; Output Parameter: ; ad_work_voltage MEAN_VOLTAGE: CLR loop_k JMP VOLT_CHECK_LOOP_K ; loop_k indicates the sort 7

8 VOLT_NEXT_LOOP_K: CLR flag_sort_over CLR loop_n JMP VOLT_CHECK_LOOP_N ; flag indicates if sort needs exchange ; loop_n indicates end data and previous data compare count VOLT_NEXT_LOOP_N: MOV A, loop_n ADD A, OFFSET ad_voltage_buff ; from loop_n get the sort i data MOV tmp_1, A ; obtain no sort i data and store in tmp_1 INCA loop_n ADD A, OFFSET ad_voltage_buff ; from loop_n get no sort i+1 data SUB A, tmp_1 ; compare the i+1 data and i data SZ C JMP VOLT_NOT_SWAP MOV A, loop_n MOV tmp_2, A ADD A,OFFSET ad_voltage_buff MOV tmp_3, A INCA tmp_2 ADD A,OFFSET ad_voltage_buff MOV tmp_2, A MOV A, tmp_3 MOV A, tmp_2 MOV R0, A INCA loop_n ADD A, OFFSET ad_voltage_buff MOV A, tmp_1 MOV R0, A SET flag_sort_over ; temporary store the data pointer ; obtain the i+1 data store in tmp_2 ; place the i+1 data in the i data location ; place the i data in the i+1 data location ; setup data exchange flag VOLT_NOT_SWAP: INC loop_n ; increment loop_n counter, execute i+1 and i+2 compare 8

9 VOLT_CHECK_LOOP_N: MOV A, 9 SUB A, loop_k MOV tmp_2, A MOV A, loop_n SUB A, tmp_2 JMP VOLT_NEXT_LOOP_N ; loop_k used to indicate present i sort ; obtain no order data number ; loop_n indicates i sort data compare number ; not complete SNZ flag_sort_over JMP EXIT_VOLT_MEAN INC loop_k ; when i sort has finished increment loop_k and sort i+1 VOLT_CHECK_LOOP_K: MOV A, loop_k SUB A, 9 JMP VOLT_NEXT_LOOP_K ; when loop_k=9 data sorting has completed EXIT_VOLT_MEAN: MOV A, OFFSET ad_voltage_buff ; middle two groups average ADD A, 4 MOV tmp_1, A ; the 5 group in tmp_1 MOV A, OFFSET ad_voltage_buff ADD A, 5 ADD A, tmp_1 ; add the 5 and 6 group RRC ACC MOV ad_work_voltage, A ; final voltage in ad_work_voltage ; end of mean_voltage()

10 Power Calculation and Power Adjustment The electric hotplate power calculation is as follows: P=K V AD I AD, where P is the power, V AD is the voltage sample value (the above ad_work_voltage value), I AD is the current sample value (the above ad_work_current value). K is the power trimming coefficient. If the V AD I AD obtained value and the actual value has an error, then K is used for adjustment, therefore the value K V AD AD and the actual power is the same. ; power_calculation() ; Calculating working power accroding to P=K*Vad*Iad, ; where, K stands for power coefficient. ; Then adjusting power with standard power value. ; POWER_CALCULATION: ; result_hl = ad_work_voltage * ad_work_current MOV A, ad_work_current MOV data0_l, A ;( data1_l)*(data0_l) MOV A, ad_work_voltage MOV data1_l, A CALL MUL8UI ; 8bit multiply 8bit subroutine ; tmp_321 = result_hl * ad_power_coefficient MOV A, ad_power_coefficient MOV data1_l, A MOV A, 0 MOV data1_h, A ;(data1_h/ data1_l)*(data0_h/ data0_l) MOV A, result_h MOV data0_h, A MOV A, result_l MOV data0_l, A CALL MUL16UL ; 16bit multiply 16bit subroutine ; ad_work_power = tmp_321 /1000 ; calculate power level /1000 MOV A, 00h MOV data2_l, A MOV A, 03h MOV data1_h, A MOV A, 0e8h MOV data1_l, A ;(data2_h.data0_h.data0_l)/;(data2_l.data1_h.data1_l) MOV A, result1_l MOV data2_h, A MOV A, result_h MOV data0_h, A MOV A, result_l MOV data0_l, A 10

11 CALL DIV24UL ; 24bit divide 24bit routine EXECUTE_PWR_ADJUST: ; if(ad_work_power > ref_power_hl + offset_power) CLR C MOV A, offset_power ADDM A, ref_power_l MOV A, 0 ADCM A, ref_power_h ; setup power value(ref_power_h/ ref_power_l) - add offset ;(offset_power) MOV A, 80h XOR A, ref_power_h ; ref_power_h/ ref_power_l setup power value MOV tmp_3, A MOV A, 80h XOR A, result_h SUB A, tmp_3 ; determine if actual calculated power value > ; (setup power level + offset) JMP PWR_BLWMAX SNZ Z JMP PWR_LGMAX MOV A, ref_power_l SUB A, result_l PWR_LGMAX: DEC PWM0 NOP MOV A, PWM0 SUB A, MIN_PWM0 INC PWM0 ; if actual power > setup power then reduce PWM ; determine if PWM0 is reduced to smallest level ; if PWM0 is already reduced to smallest value then no ; change PWR_BLWMAX: ; if(ad_work_power < ref_power_hl - offset_power) CLR C MOV A, offset_power ADD A, offset_power MOV tmp_3, A ;(offset_power*2) register tmp_3 中 MOV A, ref_power_l SUB A, tmp_3 MOV ref_power_l, A CLR tmp_3 MOV A, ref_power_h SBC A, tmp_3 ; setup power level value minus offset (offset_power*2) MOV ref_power_h, A 11

12 MOV A, 80h XOR A, result_h MOV tmp_3, A MOV A, 80h XOR A, ref_power_h SUB A, tmp_3 JMP EXIT_POWER_CHK SNZ Z JMP PWR_BLWMIN MOV A, result_l SUB A, ref_power_l PWR_BLWMIN: INC PWM0 NOP MOV A, PWM0 SUB A, MAX_PWM0 SZ C DEC PWM0 ; if present power level > (setup value offset) ; and < (setup value + offset) then no need to adjust power ; actual power level greater setup value ; if actual power value > set value then reduce PWM ; ckeck if PWM0 has increased to largest value ; if PWM0 is reduced to lowest value then do not change EXIT_POWER_CHK: CLR C MOV A, offset_power ADDM A, ref_power_l MOV A, 0 ADCM A, ref_power_h ; end of power_calculation() ; because the compare process changed the power value ; return to the setup value 12

13 In the following power adjustment programs, for the multiplication and division routines, at the beginning of these routines the input and output parameters must be declared, before calling. ; mul8ui() ; Function description: ; 8 bits multiply 8 bits. ; Input Parameter: ; multiplicand: data0_l ; multiplicator: data1_l ; Output Parameter: ; result: result_h.result_l MUL8UI: CLR result_l CLR result_h MOV A, 08h MOV loop_i, A RRADD: CLR C RRC result_h RRC data1_l JMP RR1 MOV A, data0_l ADDM A, result_h RR1: SDZ loop_i JMP RRADD RRC result_h RRC data1_l MOV A, data1_l MOV result_l, A ; end of mul8ui() ; mul16ul() ; Function description: ; 16 bits multiply 16 bits. ; Input Parameter: ; multiplicand: data0_h.data0_l ; multiplicator: data1_h.data1_l ; Output Parameter: 13

14 ; result: result1_h.result1_l ;.result_h.result_l MUL16UL: CLR result_l CLR result_h CLR result1_l CLR result1_h MOV A, 10h MOV loop_i, A rradd16: CLR C RRC result1_h RRC result1_l RRC data1_h RRC data1_l JMP rr116 MOV A, data0_l ADDM A, result1_l MOV A, data0_h ADCM A, result1_h rr116: SDZ loop_i JMP rradd16 RRC result1_h RRC result1_l RRC data1_h RRC data1_l MOV A, data1_l MOV result_l, A MOV A, data1_h MOV result_h, A ; end of mul16ul() ; div24ul() ; Function description: ; 24 bits divided by 24 bits. ; Input Parameter: ; dividend: data2_h.data0_h.data0_l ; divisor : data2_l.data1_h.data1_l 14

15 ; Output Parameter: ; quotient: result2_h.result_h.result_l ; remainder: result2_l.result1_h.result1_l DIV24UL: CLR result_l CLR result_h CLR result1_l CLR result1_h CLR result2_l CLR result2_h MOV A, 18h MOV loop_i, A SZ data2_l JMP start24 SZ data1_h JMP start24 SZ data1_l JMP start24 start24: SZ JMP div24 SZ JMP div24 SZ JMP div24 data2_h data0_h data0_l div24: CLR C RLC data0_l RLC data0_h RLC data2_h RLC result1_l RLC result1_h RLC result2_l MOV A, result1_l SUB A, data1_l MOV tmp_1, A MOV A, result1_h SBC A, data1_h MOV tmp_2, A MOV A, result2_l SBC A, data2_l JMP next24 MOV result2_l, A 15

16 MOV A, tmp_2 MOV result1_h, A MOV A, tmp_1 MOV result1_l, A MOV A, 01h ADDM A, data0_l MOV A, 00h ADCM A, data0_h ADCM A, data2_h next24: SDZ loop_i JMP div24 dispa24: MOV A, data2_h MOV result2_h, A MOV A, data0_h MOV result_h, A MOV A, data0_l MOV result_l, A ; end of div24ul() Conclusion In this application we introduced the circuit design principles of current and voltage sampling for electric hotplate applications. The application also provided current sampling filter functions and voltage sampling software source code. Finally it was shown how to calculate power values based on the current and voltage values thus adjusting the power levels. 16

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