I have a wired thermometer that I mainly use for roasts, which can support the entire probe inside the meat. However, I used it last night to cook some country style ribs (pork) and was only able to insert the probe about half-way into the rib. It wasn't touching any bone and when I calibrated it, it still read true. Anyway, when the alarm went off on the pork (I set the alarm for 160 expecting the temp to coast up to 165), it was still massively underdone. The probe lacks the dimples that I am familar with on my instant read thermometers and I would like to know if anyone has run into a problem like this before. All I can think is that the heat from the oven was being read off the back side of the probe. The tool is so useful that I would hate to regulate it to roast only duty but I have no idea how to fix this so it will work accurately.
I'm going to assume that "country style ribs" are the ones where you cut them apart first before cooking ... I'd wager a guess that everything is near bone, and a thermometer might have problems with this particular dish. If nothing else, as you can't insert it deeply enough into the thing you're taking a measurement of, there might be enough conduction along the probe for the oven temperature to throw off the reading.
Could you tell us how far the probe was in the meat? I'd assume anything less than about 1/3 the probe might be problematic, with 1/2 or more being better.
All of that being said, are you sure it's an issue with the placement of the probe, and not a problem with the probe itself?
I've had a number of them go out over the years. I've actually given up on them, and gone back to an instant read thermometer, as I'm up to 4 of the bases (can still use 'em as a timer), and no working probes. (if anyone knows any brands that sell the replacement probes individually, or even better in multi-packs, I'd be willing to go back to using them)
To calibrate -- mix some ice water, and put the probe in there. It should read 32F or 0C. (if it even goes that low, not all do). Boil water, and read the temperature of it, and it should read near 100C or 212F (possibly lower, if you're above sea level). Compare it to another room thermometer after it's been sitting for a bit ... they should read the same.
Don't try to put it into the oven directly ... you could melt the probe ... that's how I lost the first one, so you can't try to compare it to your oven thermometer.
My theory is that the probe should be inserted into the part of the meat that will be the last to heat up. For a roast without bones, that will be pretty much be the center of mass.
For something with bone it, I would aim for a point somewhere between halfway and 2/3 the distance from the skin to the bone in the place where that distance is the largest.
Are you checking the temperature while the meat is still in the oven/on the grill? For a large meat where the entire probe is in, there will be no effect. But for a thin piece of meat with just the tip inside the meat, the air temp and radiated energy will throw off the results. Either insert it length-wise in between the ribs, or set the ribs on the counter to check the temp.
If you are still getting inaccurate results after this, then I would suspect the accuracy of the thermometer.
For something like rare roast beef (off the bone), then i wouldn't insert the probe more than 2 inches. If you inserted it all the way to the middle and then set your temperature alert for rare roast beef, only the middle would be rare. if I have a large piece of topside (4-5lbs) for instance I put the probe about two inches in and set the temperature for 131 F. then when it reaches that temperature I take it out of oven and let it rest for at least half an hour, even an hour is fine. This way the beef is rare all the way through apart from about an inch at each end, but by letting it stand, it isn't raw in the middle.
I think @Joe is right that a thermometer is not going to work well for pork ribs - But this is not because the bones will interfere with the thermometer.
Rather, it is because ribs really need significant time to cook; the flesh, heavy in fat and connective tissue, does not simply come up to a temperature like an egg or a tenderloin does; it needs to be held at temperature for quite a few hours to soften. Note, it doesn't have to be a terribly high temperature however.
I developed a standard for baby back ribs with a dry rub, of 2 hours 45 minutes at 95˚C. This was based on a Youtube video of some people cooking pork ribs in a smoker (https://www.youtube.com/watch?v=Fb9roj9CaxY). The connective tissue works out for me the same as in the video even though, of course, I don't get the flavour imparted by a smoker.
If I cook the pork ribs covered in fluid, then I cook them for two hours at 200˚C, then cool and cut them, and reheat dry at 150˚C until the oil is bubbling on the surface.
With electric thermometers, the temperature sensor is usually in the tip, so you shouldn't need to insert more than about half an inch, depending on model. Analog meat thermometers need several inches.
If you're lucky, your thermometer's instructions say. For example, a Thermapen needs 1/8 in according too its instructions.