microwave laboratory architectures, planning and ... presentation-105.pdf · microwave laboratory...

An Engineering Perspective Of…

Microwave LaboratoryArchitectures, Planning and Methodology

For Food Safety

June 21, 2012International Microwave Power InstituteAnnual Symposium Las Vegas NV USA

Steven J. DruckerChief Technology Officer

Microwave Science JV LLCNorcross GA USA

[email protected]

© Microwave Science JV LLC 2012


• IEC Testing Protocols

• Microwave Oven Selection

• Voltage, Power Factor and IEC Oven Power

• The Multi-Disciplinary Challenge

• Q&A and Equipment Demonstration

Microwave Laboratory Architectures, Planning and Methodology For Food Safety


Why a sound IEC oven testing protocol matters:

IEC testing is a several times daily NRTE foods’

Validation best practice


July 2008: the GMA

specifies IEC 60705-2006


June 2010: The U.S. DOE rejectsIEC 60705-2006 as neither accurate nor

repeatable


DOE mixed signals: IEC 60705-2006 best for

ovens but IEC 705-1988 best for food?


June 2012. DOE invites comment re the incorporation of the newly revised IEC 60705

protocol into its standards


Accurate, repeatable and expressive of microwave oven cooking efficiency

(Portions used by permission. © 2012 Robert F. Schiffmann. All rights reserved)

In the continued absence of a U.S. DOE standard, it is proposed that

the ‘best effort’ protocol is IEC 705-1988, modified








Could buying your ovens online be your biggest mistake?


If a single oven operates at multiple wattages as a

matter of course, could you have just one oven?


Fact: Identical model/brand microwave ovens vary greatly one to another, and each

to itself daily, in power output

15.3 Mm units microwave oven 2008 imports:

30% < 22.5L (small < 0.8 cubic feet)

15% 22.5-31L (mid sized 0.8 to 1.1 cubic feet)

55% > 31L (large 1.1 to 2.1 cubic feet)


Countertop microwave ovens 411 circa 2011:

Manufacturer . LG Tianjin

LG Tianjin

MideaLG TianjinSharp (Malaysia)LG Tianjin

GalanzMidea


Caution:

Don’t buy the same oven twice!








Do microwave ovens exhibit chronic unexplainable multiple personality disorder?

—e.g. 1100 watts on the box, 850 IEC watts over morning coffee, 750 IEC watts mid-afternoon and 900

IEC watts on Sunday!

http://www.powerqualityworld.com/2011/04/ansi-c84-1-voltage-ratings-


Power company voltage varies within bounds set forth by the American National Standards Institute (‘ANSI’) in concert with

NEMA and EEIS


What does it mean to food safety and IEC oven power

if your wall voltage ranges from 106VAC to 127VAC—

even before the effects of AC power factor?

Power Factor—AC is not DC—or why you should care

In an ideal DC current world, all power is ‘Real’.

In the real AC current world, however, plug an electrician’s voltmeter into an outlet, and what you measure is something called Apparent Power, often far greater than ‘Real Power’.


Understanding AC Power Factor debunks

the myth that microwaves differ night and

day absent rhyme or reason

Power Factor—the IEC testing ‘Eminence Grise’“The power factor of an AC electric power system is defined as the ratio of the real power flowing to the load to the apparent power in the circuit, and is a dimensionless number between 0 and 1. “Real power is the capacity of the circuit for performing work in a particular time. Apparent power is the product of the current and voltage of the circuit. “Due to energy stored in the load and returned to the source, or due to a non-linear load that distorts the wave shape of the current drawn from the source, the apparent power will be greater than the real power.”http://en.wikipedia.org/wiki/Power_factor


Fluorescent lights, pumps, motors and refrigerators greatly

influence power factor…how many of what sizes are near your

laboratory or home kitchen?


Perfection is not an option

A $3k solution may buy you 75%

A $30k solution then would buy you 76%

There is NO 100% solution to the influence of AC power factor

Power Factor management is an asymptote !

Power (hp) Speed (rpm)Power Factor For AC Motors1/2 load 3/4 load full load

0 - 5 1800 0.72 0.82 0.845 - 20 1800 0.74 0.84 0.8620 - 100 1800 0.79 0.86 0.89100 - 300 1800 0.81 0.88 0.91

Asymptote (rhymes with anecdote, antidote, assault

boat, billy goat, cashmere coat, casting vote, creosote,

dead man's float, entrecôte…)

Best practice for management external to the microwave* of AC power factor and

Mains Voltage variations:


DO NOT use a voltmeter—plug-in, clamp on or a Simpson

REPEAT: DO NOT use any kind of electrician’s voltmeter

Use a 2500 KVA digital wattmeterSet the wattmeter to read out in VOLTS

Use a 2500 KVA AC variable transformer (‘Variac’).Before every test, ADJUST the Variac so the WATTMETER

reads 120V (or the desired voltage)

(* But are there NRTE food safety voltage compensation

solutions inside of ovens for use outside the lab?...)


STACO ENERGY Variable AC transformer 2500 KVA


Match Variac and Digital Wattmeter

KVA design capacities


Amps are NOT Kilovolts-Amps (KVA)Match KVA capacities for microwave

oven design loads

Variac, Wattmeter, Microwave Oven Hookup:

1. Plug Variac into the wall

2. Plug digital wattmeter into the Variac

3. Set the digital wattmeter to read out in Volts

4. Plug microwave oven into the digital wattmeter


Before every IEC test and NRTE food validation and before you initiate cooking,

adjust the Variac so that the WATTMETER reads 120V with microwave oven at rest

Mains Voltage Influence On Microwave Oven Power Within ANSI C.84.1 Voltage Ranges

106, 113, 120 and 127 Volts AC Mains Supply

Testbed & Protocols1100 and 1200 watt countertop ovens from Emerson, Frigidaire, GE, LG, Kenmore,

Magic Chef and SharpMains Voltage 120VAC (legged down from three phase office park supply)

Staco 2500 KVA Variable AC TransformerGlobal Specialties 2600 KVA Digital Wattmeter

Protocol: IEC 705-1988 (Modified)Three reps per oven per voltage per test

Fluke 52 and Type ‘K’ thermocoupleNIST Thermocouple Calibration



127V 120V 113V 106V

MWO 1 930 877 795 671MWO 2 951 871 755 673MWO 3 948 897 776 636MWO 4 937 871 740 644MWO 5 922 876 720 587

Avg. 937 878 757 642Avg.

Power Change

From 120V

7% 0% -14% -27%

IEC 705 (Mod.) 1100 Watt Oven Wattage

At 120V, tested wattage is less than

labeled wattage, as expected


Labeled Wattage 113V 106V 127V

MWO 1 1100 997 841 1166MWO 2 1100 954 851 1201MWO 3 1100 952 780 1163MWO 4 1100 935 814 1184MWO 5 1100 903 737 1157

Avg. 1100 948 805 1174Avg.

Power Change

From 120V

- -14% -27% 7%

IEC 705 (Mod.) 1100 Watt Oven WattageVirtual 'Box Wattage'

Normalized to their Labeled Wattage…all five microwave ovens exhibit multiple personalities—700 watts to 1200 watts. Which one is correct, and how often will which

one(s) cook safely?


127V 120V 113V 106VOven 1 987 887 750 605Oven 2 960 880 808 699

IEC 705 (Mod.) 1200 Watt Oven Wattage

Labeled Wattage 113V 106V 127V

Oven 1 1200 1015 818 1335Oven 2 1200 1102 953 1309

IEC 705 (Mod.) 1200 Watt Oven WattageVirtual 'Box Wattage'

Two 1200 watt ovens, from the same OEM factory,identical inside and out except for front fascia and brand name

The rule, not the exceptionA single oven operates with multiple personalities

Identical model/brand microwave ovens vary greatly one to another, and each to itself daily, in power output








Consultants: It takes a village.

The future of food safety is very much in our hands.

Were the impact of NRTE food safety incidents not nearly so immense, few of us would even be here.

(From the grave of philosopher, essayist, poet, and novelist George Santayana)









Multi-point temperature measurement


Microwave LaboratoryArchitectures, Planning and Methodology

For Food Safety

June 21, 2012International Microwave Power InstituteAnnual Symposium Las Vegas NV USA

Steven J. DruckerChief Technology Officer

Microwave Science JV LLCNorcross GA USA

[email protected]

© Microwave Science JV LLC 2012

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