Hi,
your problem should be to adjust to physical reality, then you may
be able to control you TBOLT temperature.
I cannot remember the term in a PID equation that accounts for time
delay.
In fact there is not one! It is the wrong algorithm for controlling
almost any heater!
It is excellent for driving pens in pen recorders where mass,
velocity and position
are the terms.
Thermal control must face some nasty delay functions, like Gauss's
error function.
When the temperature error signal is delayed, as in the TBOLT, your
best control algorithm
uses the inverse transfer function of the thermal system to predict a
somewhat tardy response.
An alternative method that works very well is to create an isothermal
wall around the TBOLT
which is held at constant temperature. I would suggest your light
bulb and a small
computer fan to create a local tornado of air around the TBOLT and by
controlling the
air temperature you will control the entire case of the TBOLT. This
will have much
faster response and may control the case of the OCXO, voltage
regulators and not
just the temperature sensors.
There, I have had my 2c worth,
cheers, Neville Michie
On 27/08/2009, at 5:56 AM, WarrenS wrote:
This can also be made to work on the TBolt units that have the 1/2
deg course Temp sensor.
The control loop gets a bit trickier, but it can hold the Temp very
close at one its course transitions points.
This would come in handy for those not wanting to change their
sensor to the high resolution type.
Another useful feature to add to a completely independent micro
controller so that it needs no other inputs is to have its program
smart enough to automatically and slowly readjust its set point
control Temperature to just above the highest day to day Peak temp
it sees. Needs no extra inputs, It just needs to monitor its own
PID loop to see if it even comes out of control due to excess temp.
Note you do not have to pass anything thru or output any RS232,
just the ONE bit if the micro is going to control the temp out bit.
It just needs to pick up the Tbolt output data in parallel and
capture the Temp info.
If the micro is not doing the Temp control then there is no need to
have the extra micro.
ws
********
Don Latham djl at montana.com
Wed Aug 26 17:38:21 UTC 2009
Heck, Warren, I'll put it on the line :-). Use a very simple and
cheap
processor such as a Picaxe, pass the rs232 through it to Lady
Heather etc,
and capture the temperature, using it appropriately. Should work
nicely
and keeps the temp control local. Even put a little LED on it to
indicate
state.
Don
**************
TBolt Nuts
To keep My TBolt's temperature constant so that the environment has
minimal effect on it,
I use an aquarium temperature controller (modified to have low
hysteresis)
connected to a low wattage light bulb, placed in a box with the
TBolt.
It works OK and keeps the TBolt's temperature constant to well
under 1
deg.
To do it better and make it more hi tech,
I'd like to have the temperature control based on the TBolt's
internal
sensor.
What I have found works well is to use the TBolt's own RS232
temperature
sensor output data,
and with a modified PID type of S/W controller, turn an external
heater
&/or cooler on off.
The heater can be an appropriate power resistor or transistor
dissipating
up to about 4 Watt,
mounted to the TBolt case. What I use to cool the Tbolt up to 5
deg C, is
a small fan blowing
at a heatsink mounted on the top of the TBolt's case.
Turning the fan on & off with a S/W driven switch, can be used to
keep the
TBolt's
internal temperature very constant over a limited external
temperature
range.
A standard PC chip fan & heatsink may be OK, if it does not add Phase
noise due to it's vibration.
Because of the long time constant and slow response of the internal
temperature sensor,
a single digital on-off bit, updated at a max rate of once per second
works great for control,
No analog needed. To keep the hardware and interface circuit simple,
I'd like to be able to use one of the unused standard RS232 outputs,
such as RTS, CTS, DSR, DTR as the heater/cooler control bit(s).
This is no problem when doing this in a DOS program or from an added
microprocessor
that monitors the Tbolt's communications, But the question is,
can it be done in Windows in such a way that a modified existing
program
such as
Lady Heather or Tbolt monitor could control an already existing
readily
available digital bit?
Being a control person, Doing a software algorithm is the easy part.
Making Windows do any kind of non standard I/O control, is way
above my
capability.
I'd like to get feedback from a Windows expert if there is a
simple way to
control an existing Digital bit
that would be available on a PC being used in a typical setup that
is used
to monitor the Tbolt.
One way I have heard suggested is to use the sound card output,
but I'd like to keep it even simpler than that, Any suggestions?
If anyone is interested in developing a program to make an
existing stand
alone micro
or basic stamp to include this function they can contact me off
line for
some sugestions.
Thanks,
ws
******************
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