APPENDIX 5B. MICROWAVE OVEN STANDBY POWER TESTING 

REGRESSION METHODOLOGY 

TABLE OF CONTENTS 

5B.1 INTRODUCTION ...................................................................................................5B-1 

5B.2 METHODOLOGY ..................................................................................................5B-1 

LIST OF TABLES 

Table 5B.2.1 Active Element Lookup Table ............................................................................5B-1 

Table 5B.2.2 Sample Regression Table....................................................................................5B-2 

Table 5B.2.3 Sample Regression Output..................................................................................5B-2 

Table 5B.2.4 Sample Integration Table ....................................................................................5B-3 

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APPENDIX 5B. MICROWAVE OVEN STANDBY POWER TESTING 

REGRESSION METHODOLOGY 

5B.1 INTRODUCTION 

DOE considered alternate testing methods to determine standby power over a shorter 

period than 12 hours that were highly representative in order to reduce the test burden on 

manufacturers. Thus, DOE developed an algorithm by which the standby power consumption 

and line voltage are measured as the clock is cycled through all the possible digit combinations 

(in terms of active elements) and then a regression analysis is performed to quantify the impact 

of the number of lit elements (by digit) and voltage on power consumption. The results are then 

integrated across the number of minutes that each active element combination is “on” through 

the course of the 12 hours. 

5B.2 METHODOLOGY 

The test method would require that the tester enter the following 18 clock combinations 

at 15 second intervals into the microwave oven clock display: 1:11, 1:17, 1:14, 1:15, 1:16, 1:18, 

1:41, 1:51, 1:01, 1:55, 7:55, 4:55, 5:55, 6:55, 8:55, 11:55, 12:55, and 10:55. For each 

programmed time, the average line voltage and standby power consumption over a 15-second 

period are measured. The tester also determines, for each clock time displayed, the total number 

of active elements. For the purpose of calculating the active number of elements for each digit 

displayed on the microwave oven display, DOE developed the following simplified lookup table. 

Table 5B.2.1 Active Element Lookup Table 

Digit Displayed Number of Active Elements 

Blank / None 0 

0 6 

1 2 

2 5 

3 5 

4 4 

5 5 

6 6 

7 3 

8 7 

9 6 

The results are then used as inputs to the regression analysis, as shown for illustrative 

purposes with example data in Table 5B.2.2 below. The regression uses five input factors: the 

number of active elements for each digit (AE1 through AE4, assuming a four-digit display) and 

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the average line voltage in volts alternating-current (VAC), while the standby power 

consumption in watts (W) is the output. 

Table 5B.2.2 Sample Regression Table 

Clock Time Average Voltage (VAC) 

Number of Active Elements by Digit 

1 Average Standby Power (W) st 2nd 3rd 4th 

1:11 119.718 0 2 2 2 1.16308 

1:17 119.8 0 2 2 4 1.22024 

1:14 119.8128 0 2 2 4 1.22018 

1:15 119.5997 0 2 2 5 1.23941 

1:16 119.7364 0 2 2 6 1.2659 

1:18 119.7421 0 2 2 7 1.28572 

1:41 119.7179 0 2 4 2 1.21773 

1:51 119.9457 0 2 5 2 1.24857 

1:01 119.9266 0 2 6 2 1.2708 

1:55 119.8723 0 2 5 5 1.32908 

7:55 119.8025 0 4 5 5 1.38373 

4:55 119.7811 0 4 5 5 1.3812 

5:55 119.6811 0 5 5 5 1.40734 

6:55 119.7248 0 6 5 5 1.43133 

8:55 119.758 0 7 5 5 1.45239 

11:55 119.7374 2 2 5 5 1.38162 

12:55 119.6646 2 5 5 5 1.46521 

10:55 119.6489 2 6 5 5 1.48858 

The regression results consist of 6 coefficients: AE1-AE4, voltage, and the intercept. A 

sample Microsoft Excel regression result is shown below in Table 5B.2.3. 

Table 5B.2.3 Sample Regression Output 

SUMMARY OUTPUT 

Regression Statistics 

Multiple R 0.998071 

R Square 0.996146 

Adjusted R 0.99454 

Standard E 0.009197 

Observatio 18 

ANOVA 

df SS MS F ignificance F 

Regression 5 0.26235 0.05247 620.3353 4.78E-14 

Residual 12 0.001015 8.46E-05 

Total 17 0.263365 

Coefficientstandard Erro t Stat P-value Lower 95%Upper 95%Lower 95.0%Upper 95.0% 

Intercept -2.989038 0.434515 -6.879024 1.7E-05 -3.935764 -2.042311 -3.935764 -2.042311 

Volts 0.035709 0.00358 9.975633 3.68E-07 0.02791 0.043508 0.02791 0.043508 

AE1 0.047066 0.003238 14.5357 5.57E-09 0.040011 0.054121 0.040011 0.054121 

AE2 0.030723 0.001635 18.79208 2.88E-10 0.027161 0.034286 0.027161 0.034286 

AE3 0.030894 0.001898 16.28024 1.52E-09 0.02676 0.035029 0.02676 0.035029 

AE4 0.032807 0.00169 19.41726 1.97E-10 0.029126 0.036488 0.029126 0.036488 

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The five input factors are input into a small integration table which accounts for how 

many minutes each digit is displaying a given number of active elements per day. A sample 

integration table appears as Table 5B.2.4 below. 

Table 5B.2.4 Sample Integration Table 

Minutes the Number of Active Elements are on For a 

Active Given Digit per Day

Elements AE1 AE2 AE3 AE4 

Standby Energy 

Consumption 

2 360 240 240 144 0.913 Wh 

3 0 0 0 0 0.000 Wh 

4 0 240 240 288 1.367 Wh 

5 0 480 720 432 3.661 Wh 

6 0 360 240 432 2.743 Wh 

7 0 120 0 144 0.808 Wh 

Voltage 28.292 Wh 

Intercept -4.207 Wh 

Average Daily Total 33.577 Wh 

1.399 W Yearly 12.2557 kWh 

The integration table then predicts the average standby power in W, the daily total watthours (Wh) consumed, and the yearly standby energy consumption in kilowatt-hours (kWh), 

assuming stable 120 VAC input power. 

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