okay I'm going okay here we have a Rosemount model 3044 temperature transmitter this is a smart instrument so it's able to talk via the heart protocol to a computer the computer in this case is a handheld Communicator the model 375 and that talks to the heart transmitter the smart transmitter using frequency shift Cade signals uh 11 sorry 1200 HZ and 2200 Herz for binary zero and one sorry one and zero respectively what this is going to do is going to show up on the oscilloscope screen as being a waveform and right now you don't see
a waveform at all in fact what you see is just simply a straight line we are TP right now reading voltage right across the communication terminals of the transmitter and since there's no communication happening right now we just see a DC voltage and that's exactly what we see right here just a plain DC voltage I'll now go over to the heart communicator and acknowledge a few error messages this transmitter does not have a sensor hooked up and so what happens is it's not able to actually read temperature and it says that's an error and it
refuses to communicate if I blast past all these errors here it'll begin communicating we can see on the oscilloscope screen we have a little pattern there you can see ripples if I try to expand this to get a better view I turn the sensitivity up the line goes right off the screen because I have too much DC voltage this is a great application for my AC coupling I'll move that to AC and now that automatically centers the line I can turn the sensitivity up and now we see the heart waveforms these are the frequency shift
key signals representing binary zeros and ones the different heights come from the two different devices the temperature transmitter versus the handheld Communicator they do not talk with the same voltage levels so I'll go acknowledge the signal there acknowledge the alarms over here again once I blast pass all those error messages and say Yes I want to ignore the next 50 error messages now we see communication again tall signals short signals uh one is a query the other is a reply it appears the tall signal is coming from the handheld Communicator it's the one that happens
first and the shorter signal is the reply what's coming back uh to the communicator from the transmitter and you can see how messed up these signals look they don't lock in synchronized real nicely that's because the frequency keeps shifting they're frequency shift keyed signals 2200 her for a binary zero and 1200 HZ for a binary 1 and that is heart communication displayed on an oscilloscope
