A thermocouple is both a welded junction of 2 dissimilar metal wires,
and (through usage) the temperature measurement system it is part of.
The system used to have 2 junctions, one for sensing and the second in
an ice bath or other constant temperature reference. The difference in
voltage drove current through a meter. The second junction is now
(generally) replaced by a low impedance reference voltage in the meter case.
An exception is when a temperature difference is to be measured, and so
would use 2 junctions, but this seems overkill for the ECat case: why
have a controlled 900 deg separate reference?
The usual solution for a control loop is to take the voltage (or current
or digits) from the sensor, filter and amplify as needed, and compare to
a reference voltage (or number). Add lead, lag, voodoo, for stability.
Ol' Bab
On 5/27/2013 3:42 PM, Andrew wrote:
I guess the concept of a temperature-compensated reference voltage is
a brand spanking new idea for you, old chum.
Andrew
----- Original Message -----
*From:* David Roberson <mailto:[email protected]>
*To:* [email protected] <mailto:[email protected]>
*Sent:* Monday, May 27, 2013 12:39 PM
*Subject:* Re: [Vo]:Re: Constant temperature Operation of ECAT?
Come on Andrew. You need to research your old books on control
theory. Where are you mounting that fixed voltage output
thermocouple you speak of? The last time I checked the output
depended upon the temperature to which it is subjected.
Since your thermocouple will change readings as the device heats
up or cools, your reference will drift likewise. This will force
the controlled device to head toward one direction or the other.
This will be anything but constant old boy.
Dave
-----Original Message-----
From: Andrew <[email protected]>
To: vortex-l <[email protected]>
Sent: Mon, May 27, 2013 3:22 pm
Subject: Re: [Vo]:Re: Constant temperature Operation of ECAT?
What? In the control regulation, everything is represented as
either a voltage or a current (because it's, like, electronics,
duh). Normally, temperature comes out of a thermocouple and is
thus a voltage. The reference voltage, to which the actual
temperature voltage is compared in order to generate an error
signal for regulation, will be a fixed voltage representing the
set-point temperature, as _would_ be output by that thermocouple
at the set-point temperature. Why is this so hard for you to
understand?
Your characterisation of the ease of regulation of a system with
intrinsic positive feedback is grossly over-simplified.
Andrew
