Just a little history:
The operational amplifier has become one of the most used of all recent analog electronic devices, and is at the heart of the GFCI. When first introduced each operational amplifer occupied the space in an entire 19 inch rack tube drawer, contained 20 or more vacuum tubes and produced copious amounts of heat. The OP Amp has graced electronic circuits under many names, from variable gain amps, to voltage comparators, but the introduction of the "chip" was what finally brought this marvelous device into its own. Today it is possible to purchase 4 Op Amps on a single 16 pin chip for less than a dollar, and they show up everywhere from drones and robots to toasters.
When employed in GFCI's they are configured as voltage/current comparators, measuring the current flowing through both legs of the GFCI device. The slightest difference between these two simultaneous measurements is considered by the device to indicate that current has found a secondary path other than the intended and causes the GFCI to instantly trip. It has been stated that the circuit is quicker than the body's ability to sense an electrical shock, and though I have tripped many a GFCI I have yet to have been knowingly shocked in the process.
Basic Comparator diagram. As long as the two signals being compared are equal and opposite nothing happens. Any difference will however cause an immediate output triggering an associated device or circuit which in the case of the GFCI is the trip mechanism. The gain of an op amp and hence the sensitivity of the device, is very easily determined by a few external resistors and can cover a very wide range from nearly zero to approaching infinity.
The operational amplifier has become one of the most used of all recent analog electronic devices, and is at the heart of the GFCI. When first introduced each operational amplifer occupied the space in an entire 19 inch rack tube drawer, contained 20 or more vacuum tubes and produced copious amounts of heat. The OP Amp has graced electronic circuits under many names, from variable gain amps, to voltage comparators, but the introduction of the "chip" was what finally brought this marvelous device into its own. Today it is possible to purchase 4 Op Amps on a single 16 pin chip for less than a dollar, and they show up everywhere from drones and robots to toasters.
When employed in GFCI's they are configured as voltage/current comparators, measuring the current flowing through both legs of the GFCI device. The slightest difference between these two simultaneous measurements is considered by the device to indicate that current has found a secondary path other than the intended and causes the GFCI to instantly trip. It has been stated that the circuit is quicker than the body's ability to sense an electrical shock, and though I have tripped many a GFCI I have yet to have been knowingly shocked in the process.
Basic Comparator diagram. As long as the two signals being compared are equal and opposite nothing happens. Any difference will however cause an immediate output triggering an associated device or circuit which in the case of the GFCI is the trip mechanism. The gain of an op amp and hence the sensitivity of the device, is very easily determined by a few external resistors and can cover a very wide range from nearly zero to approaching infinity.
Dale in the Flatlands. "Why waste time learning when ignorance is instantaneous."
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