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Author Topic: GW Instek GDS-320 testing of Refrigerator thermostat constant temperature  (Read 2470 times)

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Online Kiriakos GR

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Intro:
This measurement started as experiment about testing the new GDS-320 Oscilloscope and multimeter, and ended as a true educating material for HVAC applications.
There is no need to say that now I feel lots of pride, about exploring in full the potentials of GDS-320 trend plot.
Now this forum topic is part of my full review as another proof of my, about testing it with real applications.


A bit of theory:

What is a Refrigerator thermostat constant temperature specification?
Well this is the temperature range which one thermostat should engage and disengage.
So practically, food preservation temperature limits of very sensitive food, as for example eggs and dairy products must always keep in their very specific and safe temperature range.
Suggested temperature for eggs is at 0-5 Celsius and for dairy products the recommendation is 4-8 Celsius.
The placement of food at specific refrigerator cooling zone will warranty best results regarding lower temperature.

My very own story:
At winter time I did pull out the plug of my refrigerator that is a nice LIEBHERR KTS1414 which has the right size for my needs and also is energy class A, this also translates that it did not come cheaply.
Before activating it for the new summer period I did a thoroughly cleaning of it, and before adding anything in it I thought to simply monitor it temperature.
An actual temperature setting is not possible with analog thermostats, and even these refrigerator instructions was advising to adjust the knob at the middle point between min and max setting, and to add corrections’ later on if needed.

This refrigerator testing become my opportunity about making GDS-320 to operate by been connected with it AC mains power supply for a complete 24 hours cycle.
Other than making measurements with it, this worked also as major stress test for all it components.


How actual measurement results they get translated:

Basically what I did is to use three of equipment at my measurement.   
BRYMEN BM869 with it dual thermocouple ability was serving as monitor of refrigerator freezer compartment and also of this refrigerator normal compartment.
GDS-320 was set to record at Trend plot with the preset about collecting and presenting measured values of the past six hours.
Lastly I did use and my 50:1 infrared temperature gun about confirming with it occasionally the measurement of my thermocouple probes, and for best results I did placed an dead analog Ampere meter in the refrigerator compartment because of it black color, this helps about getting  more accurate temperature measurements’.
My own pictures bellow clearly demonstrating the power of GDS-320 Trend plot.
This created pattern of collected data represents three cycles of thermostat activation.
GDS-320 has date and time stamp, here simply holds time information of its event as soon you activate HOLD mode, in this mode you may use an orange marker and to move it with your finger over the graphed values of interest.
This gives additional information of time between recorded values and also of the actual measurement in Celsius.
I did skipped making a very fine adjustment of compensation at GDS-320 connected thermocouple as the plan was to verify High/Low limits of the actual thermostat (5C constant temperature specification).

My measurements’ proved to me a perfect operation of thermostat by examining absolute Max peaks and absolute Min peaks of all recorded cycles of thermostat activation.
And naturally useful information is the needed period of time which the refrigerator requiring between individual active cooling cycles.
This measured to be about 2:15 minutes with an empty refrigerator.

Unfortunately for now GDS-320 actual Min/Max temperature measurement due a firmware bug does not retain the actual Min/Max values at long duration trend plot recording session, when this gets fixed soon, even absolute Min/Max will offer additional gain as information in such measurements’.   
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Online Kiriakos GR

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Two years time needed for GW Instek so to deliver new firmware this be corrected.

I did this time:  Freezer compartment testing  (and this explain bellow-zero temperatures) .   ;)
WWW.ITTSB.EU   Industrial Test Tools Scoreboard  (Product Reviews Blog) / Editor in Chief.
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