4 ms·

Interesting. That makes sense, but what’s the reason for using current instead of voltage as the variable?

by crgwbr 4y ago

mschuster91 4y ago
Current flow is independent of wire length, the sender only has to turn up the voltage high enough to overcome the wire resistance.
- sjruckle 4y ago
  Also, there's greater immunity to interference and poor connections.
- adrian_b 4y ago
  This happens because the real insulators are better approximations of ideal insulators, than real conductors are approximations of ideal conductors. In electrical circuits made with normal conductors and insulators, e.g. copper wires and organic polymer insulators, it is possible to ignore the currents that branch from the wires and close through the insulators, because they are extremely small (e.g. in the femtoampere range), but frequently it is not possible to ignore the voltage drops along the copper wires, which are caused by the resistances of the wires, and which may be in the millivolt range.
  - lisper 4y ago
    I have a bachelors degree in electrical engineering and work experience in hardware design and in the back of my mind I've always known this to be true, but this is the first time in my life I've ever heard anyone say this explicitly. EE pedagogy is badly broken in places.
    - freedomben 4y ago
      Indeed, when discussing theory we love pretending that there's no voltage drop from the wires, which can really bite you when you get into design or deep failure analysis. All good technicians and engineers learn this reality fairly soon, and it's one of the things we check especially when dealing with indeterminate failures. As much as I love academia, I really wish there were more instructors with real experience that could say things like, "for math purposes assume a zero-loss conductor" while still emphasizing that real life is not so simple.
      - deepspace 4y ago
        Maybe it has to do with the culture at specific schools. As I mentioned in another comment, my instructors loved to include wire resistance in their problems, and always explicitly stated the zero-loss assumption when applicable. We did have a healthy incubation program, where instructors helped companies with product development, so perhaps that is what brought the real-world experience.
    - deepspace 4y ago
      As another EE, I had the opposite experience. Voltage drops due to wire resistance and transmission losses were drilled into our heads at any possible opportunity.
      - hermitdev 4y ago
        Difference between focusing on digital vs analog, maybe? As another EE, I vaguely recall this being pounded into us more in power systems than any of my digital electronics courses.
        ip26 4y ago
        Sounds like you missed the “actually, all those digital wires are transmission lines” class :)
    - mschuster91 4y ago
      > EE pedagogy is badly broken in places. Generally, the biggest problem with math, physics and chemistry is that if you miss just one lesson (no matter if you physically miss it, or in worst case miss out understanding a concept for a couple minutes), you can easily end up "left behind" for years. With history, arts, languages, a number of computer science topics or most of biology you can either skip out on a certain subject or catch up easily on your own, but not getting a specific part in math/physics/chemistry and lacking the resources to follow up is setting oneself up for exponential learning gap later on. The societal problem is that we've not set up schools or universities to deal with this "failure mode". Privileged kids can have after-school teaching or siblings helping out, but most will sooner or later resign and hate these subjects for the rest of their lives - and that is incredibly sad.
      - nrb 4y ago
        If only we had the technology to somehow record lessons for later viewing or for refreshing knowledge later, and additional catch-up materials & deeper dives into the topics. This seems like extremely low-hanging fruit. Why do I get a sneaking suspicion that few in the machinery of education want this, as it is a fast-track to continuous accountability?
  - BenjiWiebe 4y ago
    You will also get voltage drops from the sensors using power along your current loop as well, no? Whereas current will be the same along the entire loop all the time.
tfigment 4y ago
1-5 V is also common. You can convert between the 2 with a resistor.
SnowHill9902 4y ago
Charge is conserved whereas voltage (i.e. electric field differential) is not.
akelly 4y ago
High impedance (low current flow) signals are more prone to electrical interference. This is particularly bad when you're running long wires across a factory with big electric machines running. And if your signals are low impedance (significant current flow), then you get voltage drop across your long wire, so you can't use voltage-based signaling.

Interesting. That makes sense, but what’s the reason for using current instead of voltage as the variable?

by crgwbr 4y ago

Interesting. That makes sense, but what’s the reason for using current instead of voltage as the variable?

Current flow is independent of wire length, the sender only has to turn up the voltage high enough to overcome the wire resistance.

sjruckle 4y ago
Also, there's greater immunity to interference and poor connections.
adrian_b 4y ago
This happens because the real insulators are better approximations of ideal insulators, than real conductors are approximations of ideal conductors. In electrical circuits made with normal conductors and insulators, e.g. copper wires and organic polymer insulators, it is possible to ignore the currents that branch from the wires and close through the insulators, because they are extremely small (e.g. in the femtoampere range), but frequently it is not possible to ignore the voltage drops along the copper wires, which are caused by the resistances of the wires, and which may be in the millivolt range.
- lisper 4y ago
  I have a bachelors degree in electrical engineering and work experience in hardware design and in the back of my mind I've always known this to be true, but this is the first time in my life I've ever heard anyone say this explicitly. EE pedagogy is badly broken in places.
  - freedomben 4y ago
    Indeed, when discussing theory we love pretending that there's no voltage drop from the wires, which can really bite you when you get into design or deep failure analysis. All good technicians and engineers learn this reality fairly soon, and it's one of the things we check especially when dealing with indeterminate failures. As much as I love academia, I really wish there were more instructors with real experience that could say things like, "for math purposes assume a zero-loss conductor" while still emphasizing that real life is not so simple.
    - deepspace 4y ago
      Maybe it has to do with the culture at specific schools. As I mentioned in another comment, my instructors loved to include wire resistance in their problems, and always explicitly stated the zero-loss assumption when applicable. We did have a healthy incubation program, where instructors helped companies with product development, so perhaps that is what brought the real-world experience.
  - deepspace 4y ago
    As another EE, I had the opposite experience. Voltage drops due to wire resistance and transmission losses were drilled into our heads at any possible opportunity.
    - hermitdev 4y ago
      Difference between focusing on digital vs analog, maybe? As another EE, I vaguely recall this being pounded into us more in power systems than any of my digital electronics courses.
      - ip26 4y ago
        Sounds like you missed the “actually, all those digital wires are transmission lines” class :)
  - mschuster91 4y ago
    > EE pedagogy is badly broken in places. Generally, the biggest problem with math, physics and chemistry is that if you miss just one lesson (no matter if you physically miss it, or in worst case miss out understanding a concept for a couple minutes), you can easily end up "left behind" for years. With history, arts, languages, a number of computer science topics or most of biology you can either skip out on a certain subject or catch up easily on your own, but not getting a specific part in math/physics/chemistry and lacking the resources to follow up is setting oneself up for exponential learning gap later on. The societal problem is that we've not set up schools or universities to deal with this "failure mode". Privileged kids can have after-school teaching or siblings helping out, but most will sooner or later resign and hate these subjects for the rest of their lives - and that is incredibly sad.
    - nrb 4y ago
      If only we had the technology to somehow record lessons for later viewing or for refreshing knowledge later, and additional catch-up materials & deeper dives into the topics. This seems like extremely low-hanging fruit. Why do I get a sneaking suspicion that few in the machinery of education want this, as it is a fast-track to continuous accountability?
- BenjiWiebe 4y ago
  You will also get voltage drops from the sensors using power along your current loop as well, no? Whereas current will be the same along the entire loop all the time.

tfigment 4y ago

1-5 V is also common. You can convert between the 2 with a resistor.

SnowHill9902 4y ago

Charge is conserved whereas voltage (i.e. electric field differential) is not.

akelly 4y ago

High impedance (low current flow) signals are more prone to electrical interference. This is particularly bad when you're running long wires across a factory with big electric machines running. And if your signals are low impedance (significant current flow), then you get voltage drop across your long wire, so you can't use voltage-based signaling.