What happens if you try to test a FireWire cable with a broken stylus?
The stylus is generally composed of a high resistance resistor, neon tube and spring and other parts of this high resistance resistor resistance value is generally in the MΩ level, its relationship with the neon tube in series, the role is to limit the current, to avoid testing a larger current flow through the neon tube and the human body. The possibility of damage to the resistor is very small, but the resistor and the neon tube and the spring if there is poor contact between such failures, in the absence of knowledge of the fault, the pen to measure the charged body with the AC high-voltage, this time the neon tube will not be lit (or brightness is very weak), there will be a misjudgement, thus electrocuting the user. In addition, if the stylus inadvertently into the water inside, inside the more humid, at this time the pen to measure the AC220V voltage, it is also very easy to electrocution, so in the use of the stylus before the stylus should be checked before the stylus is good or bad, to confirm that there are no faults and then go to use.
With a digital multimeter instead of a stylus to determine the zero line and the fire line, you can switch its range to AC 200V voltage gear, the black pen touching the ground or wall, the red pen were in contact with the two wires, if the red pen is in contact with the zero line, the multimeter displays a very small voltage, close to 0 volts, if the red pen is in contact with the fire line, the multimeter displays the voltage is generally more than tens of volts. It is safer to measure AC high voltage in this way, unlike a stylus, which will have current flowing through the body.
① It is dangerous!
② However, the danger does not occur when you use a stylus to measure the FireWire. The high resistance resistors used in the stylus are solid-core resistors, also called volume resistors, which are divided into two categories: organic synthetic solid-core resistors and inorganic synthetic solid-core resistors. These resistors are pressed from a mixture of granular conductive materials, non-conductive powdered materials used as fillers, and binders. Granular conductive material is carbon black and graphite; non-conductive powdered material is mica powder, quartz powder, glass powder, titanium dioxide (titanium dioxide powder), etc.; binder is used in some cases using organic binder, some use inorganic binder, the aforementioned organic solid-core resistors and inorganic solid-core resistors two categories is based on the type of binder to distinguish. This type of resistor has a strong resistance to overload, high reliability, and is not easily damaged. In case of damage, it is also presented as a disconnected state, that is, the neon tube is not damaged but not bright, but the person holding the stylus to measure the firewire will not be electrocuted.
The danger of electrocution occurs when there is power in the firewire, and when the resistor of the stylus is damaged and mistakenly reports that there is no power, it is easy for a person to touch the firewire by mistake and be electrocuted!
The stylus resistor (mostly solid compression resistor, resistance value in a few M) if bad, can be divided into two cases: one is disconnected (this is more often the case), the other is disconnected.
One is disconnected (this is more), after the resistance is disconnected, the power circuit is disconnected, the stylus neon bubble no current, neon bubble does not light, easy to be measured on the circuit charged situation caused by misjudgment;
The second is a short circuit (this case is less), the stylus neon tube due to instantaneous high-pressure and breakdown (neon bubble normal operating voltage of 70V), then, the neon tube to play the role of insurance, will not cause harm to people.
