i searched for 2 days to find the manufacturer of
the in line thermometer fixture that i have had since the 70s
it was made by a company called pfefer in van nuys california
and it also has the name "flo temp" on the side.
it is white plastic and you just put your lab thermometer in the side
there is a threaded hollow shaft that secures the thermometer
and a threaded 1/4" outflow on the base and it clamps on to the end of your gooseneck faucet ...
but ... i couldn't find the fixture, or anyone who sold anything similar
to it ....
i did find a 60$ in line thermometer just like another one i have
you just put hose in 1 side and out the other.
the one i have worked ( works ) well and i never had trouble with it.
( i just googled in line thermometer on google to find it )
good luck !
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I used a flo temp. B&H show it here but I don't think they sell it any more:
Originally Posted by jnanian
It's important to understand the difference between accuracy and precision; the first is the error with respect to some absolute standard, and the second is the measure of the smallest change that can be reliably detected. For darkroom work, and accuracy of 1 C (about 1.8 F) is overkill (other things will affect your process more than that) but a precision of 1C means that successive runs could differ by about 4 F without your being able to tell, and if this much variation is acceptable you probably don't really need a thermometer
That having been said, the tradeoff is usually between accuracy and precision at any given price point. Thermistor thermometers are wonderfully precise, but unstable and therefore not famously accurate; thermocouples are easily accurate enough, but a readout with 0.5 F precision is pricey. The best solution seems to be to use a precise (probably electronic) thermometer to gauge consistency, and check it frequently against an accurate, stable reference (for this, nothing beats an etched-stem glass thermometer, and the Kodak Process Thermometers were designed for exactly this purpose).
You should be able to find a dial-type thermometer built for pipe-tee installation in or near your price range, and a thermistor-probe type would be even better. But plan to back it up with a good reference thermometer.
Incidentally, dial-type thermometers are sensitive to distortion of the stems, since the measuring elements are inside them. Putting one into a compression fitting is an obvious, but not very good, idea.
For what it is worth, this: http://www.thermoworks.com/products/...t/rt301wa.html would be ideal if it had a 1/8 inch stem instead of 2.5mm, so that you could just put it through a compression fitting. But there are even ways around that.
If you read the data sheet on the product above, you will see the instructions for recalibrating (which more or less confirms that it is a thermistor design) with a two-point calibration (boiling water and ice points). For darkroom work, a single-point calibration near your preferred process temperature (68 F, 75 F, or whatever) is much better, because the accuracy error is effectively reduced by the ratio of the thermometer span to the working range (180 F between ice and steam temperatures, divided by the 2 F or so that you really care about).
Having to tweak the zero point once in a while to make the device agree with your reference thermometer at working temperature is what happens when you pay $24 for a thermometer with 0.1 degree resolution
Good points greybeard. I have an excellent mercury-glass JOBO thermometer that would be reference quality, and if I had to check the in-line gauge only once a session, that would still be a boon. Assuming you could reliably know the inaccuracy of your thermometer, a gauge is a gauge.
A lot of good ideas and designs out there... I love plumbing.
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A bit more checking showed that there are quite a few thermometers of the style I mentioned that are listed as having 1/8" stems. They probably all use the same thermistor bridge/display driver IC, so the specifications (and prices) are all about the same. A pipe tee, a compression fitting, and you are in business.
The usual standard for recalibrating devices like this is every six months or so. For darkroom use, I would just run some water at the nominal temperature, check the glass thermometer, and note the display reading for the current session. When it gets off by a degree or two, get out the jeweler's screwdrivers and reset it.
The market for the cheap thermometers, by the way, is the restaurant/food service business; a "laboratory" thermometer with the same specifications is usually about 5-10 times more expensive, and a "medical" one is even more
Could you link to a suitable compression fitting? I don't have any experience with these and from what I can read about them with regards to plumbing and electrical connections I can't quite see how it would work... not that I don't believe you, I just don't fully understand.
This sounds like the easiest method by far, I'm sold.
I couldn't easily find a good illustration link, but if you go to grainger.com and look up their item # 2P236 it will be a representation of what you would use. Now 1) the Grainger item is a national brand (Parker) which is overkill for what you are doing, 2) the price is for a package of 5, approximately four more than you would want, probably, and 3) for one item like that, the handling charges will probably be more than the $3--$4 that you will pay at a local hardware or plumbing outlet. Tradiitional automotive parts stores also have these. Don't worry too much about the pipe thread size; you can use regular fittings to accommodate whatever you want to plumb the thermometer into.
Under that hex nut at the left side of the illustration would be a ring-shaped ferrule that slips over the shaft of the tube (or, in this case, thermometer) and is compressed when the nut is tightened, making a seal between the fitting body and tube. Most of these fittings have a stop surface to keep the tube from going all the way through; if you don't find one that is bored through, you can easily do this yourself. In the absence of proper tools, run the fitting into a pipe tee, and use a C-clamp to hold the tee at the edge of a bench or table while you drill. Obviously, you don't want to mess up the conical sealing surface, so it might be best to use a slightly oversize drill, entering from the far side and continuing until the stop edge is just gone and the thermometer stem will slip all the way through.
The ferrules are not reusable, but they are sold separately, so if the thermometer dies you just cut the stem, take off the nut, and use a new ferrule to install a replacement.
I can probably find one of these fittings in my artifact collection and take some d*****l snapshots if the foregoing doesn't make it clear enough.
I was in the same situation when I built my darkroom. I spent some time looking around in Ace Hardware and came up with the approach shown in the photos.
I use this to monitor the temperature to my print washer. Note that it has to be installed on the low pressure side of the valve. Otherwise on first use, the thermometer will be propelled across room.
I made my own washers for this thermometer. My first thermometer had a stem with a larger diameter, and I was able to use store-bought washers. I use two washers together to get a better seal.
Last edited by Neil Poulsen; 10-26-2010 at 10:36 PM. Click to view previous post history.
Neil, that's a nice solution. I've seen that gray hub at my Ace as well, and it's cheap to boot. Using it on the low pressure side doesn't seem like it'd really be a hindrance; that's something to consider.
Thanks for posting the pics!