To determine the length of an M12 Rigid Probe and a ThermaLock Fitting, it should be noted that the size of the probe goes hand-in-hand with the size of the fitting.
M12 Rigid Probes are sized to fit the ThermaLock Fittings they will be installed into. Therefore, both the length of the probe and the length of the fitting depend on the size of the container to be tested.
For containers where the fitting and probe will be installed into the side wall, such as cans, plastic cups, or recart packages, they should be sized to reach the middle of the container (or half of the diameter of the container).
For containers where the fitting and probe will be installed into the top lid/cap or from the bottom, such as glass jars, the "cold spot" of the container must be known. The fitting and probe are then sized so the sensing tip is at the cold spot of the container. If you are not sure of the cold spot in your product, you may need multiple lengths to conduct a "cold spot study."
Note: Fitting lengths are measured from the tip of the probe sheath to the end of the face where the probe will be installed.
To measure your container, consider the outermost point of the container side wall, bottom, or cap, and measure to the desired location where the sensing tip will be located.
For example, if the can is a 308 diameter can, which translates to 3 - 8/16", the probe/fitting length to reach the middle of the can should be one half of that dimension, or 1 - 12/16".
Or if a glass jar is 5" high, and the cold spot is 1" above the bottom of the jar, the probe/fitting length would be 4".
It should be noted that the length of the fitting is actually about 0.12" longer than the length of the probe, to compensate for potential positional uncertainty of the RTD sensing element on the probe.