signal generators, devices such as the CM-458/U Signal Comparator were used (which tested the DCU-201 or DCU-218 Aircraft Controller, which passed the unique signal to the weapon's MC2969 intent strong link), which would check that the signals that would be passed to the strong link were correct. The CM-458, built by Sparton Technology, tested voltages, pulse widths and signal sequence against the fixed sequence for the strong link, and was mounted on the aircraft pylon in order to also test the aircraft wiring. Weak links The weak links, which follow the strong links, are designed to fail earlier than the strong links. There are many kinds of weak link, which are sensitive to conditions including thermal, electrical or mechanical problems. Some weak links are dedicated devices inserted into the signal paths that function only as weak links, and others can also be critical parts of the weapon that are designed to become inoperative under certain conditions. An example of a weak link that is sensitive to temperature are the capacitors in the firing set which are charged in order to then discharge to trigger the detonators. These can be deliberately designed to fail when a specific high temperature is reached, which will prevent the firing set from being able to detonate the explosives. Limitations These mechanisms do not prevent misuse of the weapon, which is restricted by Permissive Action Link code systems, or an accident from physically causing initiation of the explosives or detonators directly from extremely high temperatures, impact forces, or electrical disturbance such as lightning. The risk of accidental direct detonation is significantly reduced by using insensitive high explosives such as TATB, which is extremely unlikely to detonate due to fire, impact or electricity. While TATB may decompose or burn in a fire, it is extremely unlikely to detonate as a result of that decomposition or burning. See also Nuclear weapon design Permissive Action Link References Nuclear technology Nuclear weapon safety