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Chart Recorder and Its Replacement

Pax Electronica
 

I apologize in advance for this question not being specific to Tektronix. But I think many of you are familiar with what I am about to ask.

In old instruments, the output is often send out to a chart recorder. The signal is typically sent through two connectors, one of them is kept at ground. I suppose the recorder would need special signals for "start recording" and "end recording". Can someone explain how this is done?

Thanks.

Daniel Koller
 

Hmmm....  I can't think of any specific instruments that I have that do this, but I have used some in the past.  But in general, one outputs to an X-Y recorder, to be specific.  The only functions the instrument needs to output are X-out, Y-out and Pen_Down.   Most if not all HP X-Y recorders have a Pen-Down pin on a rear connector.  The output from the instrument is then generated with simple vector graphics.
  I suppose you could use a strip-chart recorder with time as the X-axis for things like scope plots, but then you need an appropriate sweep speed and instead of a pen_down line, you need a sweep_enable line.   Various strip chart recorders also have such a feature as an external input.  You could sync a very slow sweep from an oscilloscope to the chart recorder.  
  If, for example, you wanted to output the trace of a 545 oscilloscope, for a slow sweep (one taking a few seconds to sweep the screen) you could do it two ways.  1) Connect the sweep output to the X input of an X-Y recorder, the Vertical signal Out to the Y input, scale both accordingly, and connect the A gate output to the Pen_down line.    OR, you could use a strip chart recorder.  Connect the A gate to the sweep_enable function, and the Vertical output to Y in.  
Dan

On Monday, October 14, 2019, 11:19:36 PM EDT, paul.delamusica@... <paul.delamusica@...> wrote:

I apologize in advance for this question not being specific to Tektronix. But I think many of you are familiar with what I am about to ask.

In old instruments, the output is often send out to a chart recorder. The signal is typically sent through two connectors, one of them is kept at ground. I suppose the recorder would need special signals for "start recording" and "end recording". Can someone explain how this is done?

Thanks.

Pax Electronica
 

Thanks! After reading your post, I looked for and found a separate connector that does provide the START signal and a RESPOOL signal for overlay plotting.

Pax Electronica
 

I did some testing on the terminals that supposedly provide the START signal. It turns out to be just a relay that closes when the recording starts and opens again when the scan is finished. The resistance goes from infinity to zero at START and goes infinity again at STOP, at least in theory. In reality, the instrument has other stepper motors going on and off. When that happens, the relay seems to be unable to hold down and goes open momentarily. The interruption is short enough so that a small capacitance could solve the problem, but is that what we supposed to do? Or is it an indication of some other problems, such as power supply going weak?