generic pause/wait?

The structure looks pretty tidy - although I'd really recommend doing:

Sensor.prototype.getSensorType = function ...
Sensor.prototype.getSensorAddress = function ...
// etc

Instead of your Sensor.prototype = {. It's probably more personal opinion, but it seems more pleasant than having to redefine constructor.

You've also defined getters like getSensorAddress, which is fine - however you then do a = this.getSensorAddress;. That'll return the function itself, rather than executing it and getting the result... You might also want to put a var before a, so a isn't defined as a global variable.

In your code getSensorResult returns immediately, so while you get a value in getSensorReading you're not actually returning it. For that, you'd need to use a callback:

  getSensorResult:function (callback) {
    // ...
    setTimeout(function (e) { callback(that.getSensorReading()); }, w);
  },

Then you can use it with:

ph.getSensorResult(function(value) {
  console.log(value);
});

Hope that helps!