Reading a thread here about tri-state logic reminded me of something that always baffled me, a component looking for a problem maybe? This was the majority logic gate. I cannot remember its part number, but I was wondered what its application might be.

Completely obsolete by the passage of time and the march of technology no doubt, but I wonder whether anybody has used one of these in the past, and what for.

 

Reading a thread here about tri-state logic reminded me of something that always baffled me, a component looking for a problem maybe? This was the majority logic gate. I cannot remember its part number, but I was wondered what its application might be.

Completely obsolete by the passage of time and the march of technology no doubt, but I wonder whether anybody has used one of these in the past, and what for.

Not enough to go on with super high confidence, but I'm assuming you are talking about a logic gate that takes on the state corresponding to whichever state is taken by the majority of the inputs. Also known as a voting circuit.

The usual case is you have three inputs and you output a HI if two or more of them are HI, and output a LO if two or more of them are LO. It is a very commonly used logic function when dealing with redundant systems or for performing certain kinds of error correction.

There is ambiguity if there are an even number of inputs, so the designer has to decide who wins in the case of a tie.

This is actually one of the situations in which ternary logic is a natural fit since there are three natural outcomes -- win, lose, draw.

 

Yes, that is what I meant. I can remember thinking at the time – over 40 years ago – what's that for?

 

Majority logic can be used in critical reliability applications (such as in an airplane).
For example you can have three sensors measuring the same variable, each giving an output.
If one fails, majority logic ignores the outlier, and takes the output of the other two as correct.
It can be done for either an analog or digital signal.

 

Majority logic can be used in critical reliability applications (such as in an airplane).
For example you can have three sensors measuring the same variable, each giving an output.
If one fails, majority logic ignores the outlier, and takes the output of the other two as correct.
It can be done for either an analog or digital signal.

Unless you put them all in upside down. The Majority logic is correct but you can't defeat stupid.
https://www.russianspaceweb.com/proton_glonass49.html#culprit

By July 9, it is transpired that investigators sifting through the wreckage of the doomed rocket had found critical angular velocity sensors, DUS, installed upside down. Each of those sensors had an arrow that was suppose to point toward the top of the vehicle, however multiple sensors on the failed rocket were pointing downward instead. As a result, the flight control system was receiving wrong information about the position of the rocket and tried to "correct" it, causing the vehicle to swing wildly and, ultimately, crash. The paper trail led to a young technician responsible for the wrong assembly of the hardware, but also raised serious issues of quality control at the Proton's manufacturing plant, at the rocket's testing facility and at the assembly building in Baikonur. It appeared that no visual control of the faulty installation had been conducted, while electrical checks could not detect the problem since all circuits had been working correctly.

 

The Majority logic is correct but you can't defeat stupid.

As many failures have shown in both governments and machines, not much can.