Thermometer Calibration/Jobo Processor

[Swift Raven]

I am wondering whether the temperature read out on my Jobo CPP processor is accurate and if there is a way to check it's calibration. There is a difference of .6°C between the Jobo and my tried & true Kodak Process thermometer. I don't know which to believe. It doesn't matter for B&W but the temp. tolerance for E-6 is ±.3°C. Any suggestions?

 

[rwyoung]

So leave your Kodak thermometer in the water bath and tweak the Jobo temperature knob until you are happy.

It will take some time for the temperature to stabilize. Maybe put in a tank and let it roll to swish things about. And also watch to see how much hysteresis the Jobo controller allows.

I've only ever done B&W with mine. I don't worry much about the absolute temperature since I'm going to be testing for personal EI and developing time anyway. Just always set it to 20C and wait to start a run until I hear the relay cycle a few times.

 

[hal9000]

I wouldn't trust the JOBO display. On my CPP-2 that I bought brand new just a few months ago, I need to set the temperature to 21.9° to get 20.0° according to my calibrated Greisinger electronic thermometer, which in turn matches my fever thermometer to 0.1°C.

 

[GeorgesGiralt]

Hi !
Yes, I've a suggestion !
E6 processing is at quite the same temperature than the human body. One can find very precise (because checked) thermometers centered toward this temperature at the pharmacy (drugstore).
In France where I live, I've bought a set of 3 for less than 20 USD. Each one has a little marking at 36.5 °c (I supose that this is the calibration point) and the metal scale running along the tube is of different length on the 3. They give surprisingly identical results when placed on the same bucket, and can be read AFTER pulled out of the water as they hold the reading. Last but not least they do not use mercury at all but a different metal but I don't know which one.
Try it, and you'll be satisfied, I think....
Oh, after bathing them in E6 chemistry, don't use them for medical usage ;-)
BTW, when the water bath is at 38.5 °C, the knob said 42 on my CPE2 ...

 

[rwyoung]

So leave your Kodak thermometer in the water bath and tweak the Jobo temperature knob until you are happy.

It will take some time for the temperature to stabilize. Maybe put in a tank and let it roll to swish things about. And also watch to see how much hysteresis the Jobo controller allows.

I've only ever done B&W with mine. I don't worry much about the absolute temperature since I'm going to be testing for personal EI and developing time anyway. Just always set it to 20C and wait to start a run until I hear the relay cycle a few times.

Should have mentioned, that on my unit, the dial is quite reasonable for absolute temp, within 0.5C based on two different lab grade glass thermometers. And also very good about repeatability. The thermostat seems to allow about -1C drop before it kicks in. Haven't specifically tested this, just anicdotal evidence for the hysteresis.

 

[hal9000]

My JOBO CPP-2 is extremely precise - I calibrated it when I first bought it and check the temperature every now and then and have never found more than even 0.1°C difference. But it is not very accurate - as I said, mine requires a setting of 21.9° to obtain 20.0°C. In any case since precision (reproducibility) is more important than accuracy in photography (at least in b/w), especially if you test your materials, the JOBO processor does the job extremely well. And if you calibrate against a trusted thermometer then you should achieve high accuracy as well.

 

[hka]

Here the same. I trimmed the temperature of the CPP2 exactly at 20°C. By doing that the high temperatures for E6 or C41 settings (38 or 35°C) are much higher than read on the display. These are at least 3°C to low. Reproducibility is no point if you know what to do. I develop E6 at 35.4°C and C41 at 32.4°C).

 

[Byron Worthen]

I have a CPP2 and a Kodak process thermometer. I find that for 68 F, I have to set the JOBO to 20.8 C. For 75 F I have to set the JOBO to about 25C. However, I find that once I set the temp, the JOBO holds it within a half a degree F all day. The Kodak thermometer is extremely accurate, highly responsive, and completely analogue, so I trust it as my standard.

 

[Swift Raven]

Thanks to all for your thoughtful suggestions. I thought Georges Giralt's suggestion to use a medical thermometer as a calibration standard was a good one and I will try it. It is good to know that others have experienced the same calibration issues as I have. This was my first post on APUG and it is gratifying to see responses from all over the world! Thanks to all.

 

[argus]

I have both a CPE2+ and a CPA2 and to get 38 C in the chemistry, I must set the JOBO's to 37 C.
To add to the confusion, try measuring the temperature of the JOBO water bath on different places...

Harry, you live like a risky man. Bring some of your slides on the next meeting, will you? I'll bring mine.

G

 

[rwyoung]

I have both a CPE2+ and a CPA2 and to get 38 C in the chemistry, I must set the JOBO's to 37 C.
To add to the confusion, try measuring the temperature of the JOBO water bath on different places...

Harry, you live like a risky man. Bring some of your slides on the next meeting, will you? I'll bring mine.

G

And that is why I suggested letting a drum spin to splash the water around a bit and reduce the temperature gradient...

 

[GeorgesGiralt]

Hi !
I forgot to mention that in E6 processing it is the bath temperature which is important. So do not measure the temp of the watering bath but, instead, the temperature of the first dev and color dev. Check that you stir a little once in a while to ensure good homogeneity of the solution.
If, then, you check the water bath you'll find it a little on the high side. So put some water at the fisrt dev temp. in the tank and let it roll with a thermometer inside for a couple of minutes (5 to 8 will be excellent as these are the extreme duration for the first dev bath) and then read the temp again in the tank. It should be close if not equal to the correct processing temp (the too hot of the water bath is compensated for by the too low of the air to gain an equilibrium).
When satisfied by the setting, put a nice mark on the knobs in order to be able to get the setting right the next time.
Here, the medical thermometer with it's "hold" capacity is a great help. Of course, this will not work for B&W, but IMHO, B&W is better done by hand in the silence of the lab ;-)

 

[hka]

I measure my intemperature of the dev and also when I dump it. Between these two is a difference of about 1½-2°C. So I calculated the intemp a little bit higher to equal. This is working for me.

 

[Swift Raven]

This is getting interesting. I have noticed that the water bath temperature is always somewhat higher than the chemistry. In fact it is difficult, at least in my processor, to get the water bath and chemistry to the same point. Even worse, I had assumed that the Expert drum that I use would hold the temperature of the chemistry at the same temperature as the water bath. I will be running tests this weekend to find the temperature differential. Thanks again.

 

[TheFlyingCamera]

I have an older CPA2, and gosh, is the dial setting off from the actual water temp. When I have my dial set to about 19 C (a bit below the 20C marking on the dial, my water bath temperature as measured by my dial thermometer is 75-77 F (more like 22-23 C). Because of this, I have not ventured to try any C-41 or E-6 at home. This is ok for my black-and-white work, as I have standardized my development times around the temperature gradient and I get consistent, happy results from this. I was contemplating getting a new (or at least only mildly used) CPP2 as an upgrade, but if the CPP2 is as inaccurate, I may as well just do some testing of temperatures until I can nail down what actually is the appropriate temp on my CPA's dial, and just mark the dial.

 

[hka]

When I trim the hihgtemperature (30 - 38°C) settings on the circuitboard of the CPP2 then the low temperature are beneath. If I do it the other way round then the high temperature settings are off. In other words you have to deal with it and always test for the exact grades.
BTW it's normal that the watertemp in de trog is a litle higher - about 1-1½°C) than the chemistry. But this is a constant faktor.

 

[GeorgesGiralt]

To "The Flyingcamera",
IIII do E6 at home using the Jobo (it was bought for this use).
Once you've found the setting that gets the chemistry at the correct temp, it's _really_ consistent.
And E6 becomes a matter of half an hour ...
Usually, I prepare the processor with it's chemistry in the various tanks the day above or in the early morning and I turn it on with a timer switch 3 to 4 hours before the planned return to home.
This way, when I have put the film in the tank, the processor is up and ready. Usually, before lunch I've a set of chrome hanging for drying.
A permanent marker or felt tip pen is your friend to mark the settings on the knobs.

 

[AdClem]

My replacement CPE-2 (which I bought on the popular internet auction site) came ready 'calibrated' with a felt tip mark on the dial to show where 20°C ought to be. When I checked it, I found that it's very accurately placed now.

Another innovation that I inherited, and can take no credit for, is a small submersible pond pump. It's very compact, and sits comfortably out of the way in the space beneath the motor housing. The power cable, and a tube of about 4 ft, hang out over the back edge, to which they're taped. How useful, I thought, for emptying most of the water from the unit rather than trying to tip it into the sink when full - with much of it ending up on the kitchen floor. It does do that quite well. But I soon realised its principal purpose, with the tube in the bath, is to circulate the water; which it does superbly well. The result is that it reaches working temperature in minutes and maintains a uniform temperature throughout the process.

 

[Ed Sukach]

I have been advised by the Techs at JOBO that the temperature of the tempering bath is routinely set higher than that indicated to compensate for heat loss at the tank itself. Note that the tank itself is immersed ~ 20% - 30% in the tempering bath, and additionally, there will be cooling when the chemistry is poured from the bottle into the tank itself.
If you are really interested in actual tank solution temperature, be sure that the system is stabilized at a given temperature (one hour should be sufficient), and pour an appropriate amount of water into the tank; let the tank rotate for twenty minutes or so, and *QUICKLY* remove the tank and get a quick responding thermocouple (one of the BD digital fever thermometers might be good) into the tank.

From experience, I have never found processing to be as sensitive to temperature as some would have us believe. I know that tolerances as tight as +/- 1/4 degree F have been specified, but that would take some sophisticated, high end equipment - and even then - I would not be sure of success. Even measuring that accurately would be a problem -Kodak's Lab Thermometer is only "good" for +/- 1/4 degree F - normally the measurement control system should be ten times as accurate as the system control limits - in this case, +/- 0.025F. That would require a laboratory grade thermocouple and a LOT of attention to the heat loss rheology.

I have screwed up - processing film at 35 Degrees C (forgot to reset the JOBO from RA4 color printing) to 38 Degrees C (and vice versa) - 3 degrees C (5 F) "off" - without signifcant color or contrast shifts.

This is all form my experience - the best source of information would be Photo Engineer -- are you there, PE?

 

[Swift Raven]

Test Results / Thermometer Calibration, Jobo Processor

Based on suggestions made I checked the calibration of my Kodak Process thermometer against a medical thermometer (the old fashioned max reading type). The two agreed exactly. Then I performed the following tests. each test was done after the Jobo had stabilized at temperature for 2 hours

Jobo Setting: 38°C
Water Bath: 37.2°C
Solutions in bottles: 36.4°C
Solution Temp in 3010 Drum measured with medical thermometer taped to inside: 36.2°C

Based on this I adjusted the Jobo to 39.9°C and got the following results:
Water Bath: 39°C
Solution in Bottles: 38.3°C
Solution in Drum: 38.1°C

The E-6 1st & color developer require 38°C ± .3°C
So there it is. I have my settings. Thanks to all for your help.

 

[goldenimage]

i also have a jobe which i have to set my temp a little high to get accurate readings but once its there it keeps it there, ive had great results processing e6

 

[Ed Sukach]

Based on suggestions made I checked the calibration of my Kodak Process thermometer against a medical thermometer (the old fashioned max reading type). The two agreed exactly.

That indicates that you have two thermometers that agree closely. Whether or not those points of agreement is, are fact, the CORRECT temperature, appears to be up for grabs.

I know there is a pot that regulates the temperature of the water flowing from the circulation pump into the water bath, and that would be set one degree - or so - HIGHER than the "dial temperature", as I've said, to compensate for heat losses in operation. You COULD perform surgery on the Control Unit to try to find that pot.

The E-6 1st & color developer require 38°C ± .3°C

- And in the CCP-2, the temperature regulation solenoid and heating coil activate at +/- 0.3C above or below the "set" temperature.

I am fully aware of what the Manufacturers claim to be "necessary". Over the years, I have processed E-6, C-41 (I STILL have an Anscochrome Processing Kit - from the '60's), - a variety of other stuff, - inadvertantly at the wrong temperatures.
I TRY to be precise (uniformity is more important than accuracy), but I've never really had a problem with temperature.