From whence we came, evolution of instruments and standards ASTM G26 to G155-05a
by S. Jamison, NJ Industrial Controls Opinions are mine alone
I began my career as a repair and calibration tech directly out of college in 1984. At that time there was still a fair number of 65WR instruments running in the field. The Ci65 was replacing these instruments very quickly by this time. The Ci65 had an "Ambient / Black Panel" control switch on it and I asked some questions on it's function as I knew the 65WR used the Ambient Probe to indirectly control the Black Panel Thermometer temperature by visual observation and setting.
I had some time to play around with a Ci65 at one company and I ran the instrument through a spray cycle in both control modes. I created this strip chart recording of my observations. (Please note, the paper was in backwards so the image is mirrored for clarity.)
What the chart shows is that the older 65WR's controlling BP temperature indirectly by controlling the air temperature with the damper, and the instrument goes through a spray cycle, the RH stays lower and the temperature of the air remains something close to the original set point. The BP drops and stays low during the entire spray cycle.
With the new (in 1979) style direct BP control, the damper closes and remains closed during the entire spray cycle. This locks the heat and humidity inside the instrument and both the BP temperature and air temperature rise during the spray cycle. This means the samples get much hotter, especially with older lamps running higher Wattages.
Sometime circa 1990 the first Ci65A's were shipped, they had the new "Automatic Blower Control Mode" system in them where both the Black Panel and Chamber Temperature could be controlled. This was a vast improvement, however, the instruction manual indicated this system should not be used with any cycle calling for spray (read especially ASTM G26 and SAE J1960) as the temperature profile would be changed from how a Ci65 with fixed or manually variable blower would run.
In 1995 the Ci4000 reverses this control strategy and returned to the pre 1979 type, controlling the air temperature during the spray cycle (if so programmed.) So . . . particular to G155, Ci35AW's and Ci65A's running in the required manual or fixed blower control mode cannot be compared to Ci4000 and Ci5000 instruments running the pre-loaded ASTM G26 or G155.
An additional but not inconsequential difference is ASTM G155 cycle 1 does not specify humidity control while the pre-programmed setup in the Ci4000 and Ci5000's specify 50%. This causes differences in wet time which with some types of samples which may cause differences in results. The larger difference is ASTM G155 cycle 1 specifically indicates "air temperature not controlled" which necessarily means it should be programmed for "Chamber Temperature Control: No" or "Rack Temperature Control Only."
In my opinion: The Ci4000 and Ci5000 pre-loaded programs for G155 cycle 1 do not meet the standard as written.
HOWEVER . . .
ASTM, in their bid to be inclusive, wrote Cycle 1 so as to not require the advanced control functions available only on Atlas equipment. The bare fact is that controlling both all four parameters, Irradiance, BP Temperature, Chamber Temperature, and %RH, you will get the same results today, tomorrow, next week, three years from now. By controlling both the Chamber Temperature and the %RH the instrument is controlling all types of specimen temperatures very consistently regardless of the number of hours on the lamp, and by controlling the %RH, controlling the time of wetness of your specimens. BOTH of these change radically as the Xenon Lamp ages and the lamp requires more Wattage (heat) to attain constant irradiance.
To be clear, running ASTM G155 cycle 1 as the standard requires means that specimens run during, (e.g.,) a 500 hour period with new lamp and glass may not give the same results for many measured or physical properties as when run with a lamp with 2500 hours on it.
So, if you really *must* run G155 cycle 1 to the letter of the law, and want to simulate the Ci65/Ci35 method of doing things read on . . .
On the Ci4000/Ci5000 if you program it for "Rack Temperature Control Only" or "Chamber Temperature Control No," on both the instruments have air heaters that are rather large and can in fact get the BP Temperature back up to the set point with the sprays running. It is somewhat of a conundrum.
In an effort to allow customers to run their Ci5000's like the Ci65A, this same plastics additives company spent the resources necessary for me to come up with a method of making the Ci5000 run comparably so they could use the historical data for G26 they had in hand. A pdf formatted comparison of these profiles is available here.
A pdf formatted test set up and modifications sheet is available here. This modification requires the installation of a relay to disable the air feed to the humidifier during the spray cycle, kits are available on request, documentation for "do-it-yourself" is available free and only requires one $25 relay and some wire.
On the Ci5000, the Air Heater is disabled and the results compare favorably with the Ci65A (for plastics.)
On the Ci4000 we had to add a timer which pulsed the Air Heater at about 33% to simulate the same temperature profile as the Ci35/65 if that is what you need. The standard, however, does not require this, but it may not compare favorably with its older sister, the Ci35.
