5B-i

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
5B-1

APPENDIX 5B. MICROWAVE OVEN STANDBY POWER TESTING 

REGRESSION METHODOLOGY

5B.1 INTRODUCTION

The U.S. Department of Energy (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 
5B-2

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 six 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
5B-3

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

Active 

Elements

Minutes the Number of Active Elements are on For a 

Given Digit per Day Standby Energy 

AE1 AE2 AE3 AE4 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.