Electronic circuit protectors


Senior Member
190529-1709 EDT

Several threads have popped up about electronic circuit protection being new.

It is possible that product getting to market may be new, but the basic concepts are not new.

This can be illustrated by a patent issued to me in 1967 and filed in mid 1962.

One claim reads:

"An electronic circuit protector for interrupting an electrical circuit upon the occurrence of a predetermined condition therein, said electronic protector comprising a signal responsive switch electrically connected in said circuit, and a control circuit having a time dependent characteristic for controlling the condition of said switch, said control circuit comprising means for sensing an electrical condition in said electrical circuit having an output signal, a threshold circuit for triggering upon the occurrence of said predetermined condition, a generalized function circuit for modifying said sensor means in accordance with a predetermined function, and a variable gain amplifier connected in said control circuit to control gain between said sensor and said threshold circuit for determining the trip characteristic."

There were only three patents cited for referencer, and only one predated my filing.

Has my patent been referenced by any later patents I don't know.

I don't know whether the variable gain amplifier needed to be in the claim. Outside of that the clain is quite broad. Whether this claim would read on a circuit using a digital computer to do the same function I don't know. In any event the concept of an electronic circuit breaker is not new.



Senior Member
190601-0845 EST

No one has asked any questions so far, but I think it is instructive to look at the claim for those that have no experience with patent law.

The claims of a patent are what legally define its scope.

In this claim there is a switch between an energy source and a load. Any breaker will have that. There is no definition of what the switch is, and that means no limitation. At the time of this patent the word switch generally meant a controllable on-off circuit element.

There is a time dependent control circuit for controlling the switch. Very broad, but in terms of language at that time does not read upon an electro-magnet, or bimetal thermal element. Thus, does not read on conventional breakers.

Means for sensing an electrical condition. This does not define the means or the electrical condition. It just says they exist.

There is a threshold circuit. That is a binary decision maker. It says nothing about the threshold point. Thus, the threshold could be fixed or adjustable, and it says nothing about how the threshold could or would vary with time.

A variable gain amplifier is really a variable multiplier.

There is a generalized function circuit. This does not say much in detail, thus, very broad.

There is some predetermined function. Again no detail and very broad. This simply says that before an event occurs the trip function has been defined. In other words a priori, to know before. See https://www.merriam-webster.com/dictionary/a priori

All these different things are linked together to make a breaker.

The great automotive case of Selden vs Ford illustrates how claims relate to products. The reason the Selden patent for an automobile did not read on Henry Ford's car was that Seldon's patent read on a 2 cycle engine while Ford was building a 4 cycle engine. One patent attorney told me that the case should never have gone to trial.

Some discussion at https://en.wikipedia.org/wiki/George_B._Selden .



Senior Member
I think the earlier version of electronic circuit breaker had some sensing problem.......


Batteries Not Included
United States
I think the earlier version of electronic circuit breaker had some sensing problem.......
Far from it, electronic circuit protection has been proven profoundly stable for over 40 years and makes up the majority of all protection.

The device, the first microprocessor-based digital protective relay, was developed by Schweitzer as part of a thesis project during his doctoral studies at Washington State University in the late 1970s.

The SEL-21 relay – which Schweitzer subsequently brought to market in 1984 after founding Schweitzer Engineering Laboratories in Pullman – revolutionized the electric utility industry by making it safer, more reliable and economical.