Ooooh, another exciting STAMP project!
Archiver
Posts: 46,084
Here's the current STAMP task I'm faced with... any help appreciated.
I am trying to build a device that will both monitor and regulate the
temperature of a cylinder of water, holding somewhere between 2 and 6
ounces. The temperature needs to stay at a constant setting of about
100 degrees F. Sometimes, the cylinder will be emptied, and the device
needs to be able to detect this as well. The power source will be AC
from a wall socket, though I'd prefer it to be battery powered via
some off-the-shelf variety of battery.
Any thoughts on this? As usual, writing the software is not a problem
for me, building the hardware is, and I'm a little unclear as to how
to heat water using electricity, esp if it's supposed to be regulated.
Thanks,
-Chilton
I am trying to build a device that will both monitor and regulate the
temperature of a cylinder of water, holding somewhere between 2 and 6
ounces. The temperature needs to stay at a constant setting of about
100 degrees F. Sometimes, the cylinder will be emptied, and the device
needs to be able to detect this as well. The power source will be AC
from a wall socket, though I'd prefer it to be battery powered via
some off-the-shelf variety of battery.
Any thoughts on this? As usual, writing the software is not a problem
for me, building the hardware is, and I'm a little unclear as to how
to heat water using electricity, esp if it's supposed to be regulated.
Thanks,
-Chilton
Comments
www.minco.com has some neat solutions.
Dennis
Original Message
From: chilton@t... [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=-VTQsOQq4ah7j3aosZTAkv1aBfCck6KoFQAYH4jVTnRUvfBsHkEJl-zLUqOIutn8csYeU_fHNiqQ]chilton@t...[/url
Sent: Thursday, June 07, 2001 12:00 PM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] Ooooh, another exciting STAMP project!
Here's the current STAMP task I'm faced with... any help appreciated.
I am trying to build a device that will both monitor and regulate the
temperature of a cylinder of water, holding somewhere between 2 and 6
ounces. The temperature needs to stay at a constant setting of about
100 degrees F. Sometimes, the cylinder will be emptied, and the device
needs to be able to detect this as well. The power source will be AC
from a wall socket, though I'd prefer it to be battery powered via
some off-the-shelf variety of battery.
Any thoughts on this? As usual, writing the software is not a problem
for me, building the hardware is, and I'm a little unclear as to how
to heat water using electricity, esp if it's supposed to be regulated.
Thanks,
-Chilton
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switch it from the Stamp with a Triac or SCR (opto-isolated, of course).
Apply the tutorial on PID from the Parallax web site. You'll need to
calculate the power requirement for your heater for the rate and temperature
tolerance and hysteresis of your process, but that's just some junior
engineering work. if you want to get fancy, you can phase-angle fire or
proportional time-base fire the heater for very steady results.
Chris
>
Original Message
> From: chilton@t... [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=mtIGh8f9ex793qfqH58gM1IhaHV1NFdTXV1kMwIzyfzrZ6wmWuEVwD59UuZimYZVsKDDlbHffqE]chilton@t...[/url
> Sent: Thursday, June 07, 2001 12:00 PM
> To: basicstamps@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] Ooooh, another exciting STAMP project!
>
>
> Here's the current STAMP task I'm faced with... any help appreciated.
>
> I am trying to build a device that will both monitor and regulate the
> temperature of a cylinder of water, holding somewhere between 2 and 6
> ounces. The temperature needs to stay at a constant setting of about
> 100 degrees F. Sometimes, the cylinder will be emptied, and the device
> needs to be able to detect this as well. The power source will be AC
> from a wall socket, though I'd prefer it to be battery powered via
> some off-the-shelf variety of battery.
>
> Any thoughts on this? As usual, writing the software is not a problem
> for me, building the hardware is, and I'm a little unclear as to how
> to heat water using electricity, esp if it's supposed to be regulated.
>
> Thanks,
> -Chilton
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed with. Text
> in the Subject and Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to
> http://docs.yahoo.com/info/terms/
>
>
built in, you could hack it or just use it as is.
normdoty@h...
>From: chilton@t...
>Reply-To: basicstamps@yahoogroups.com
>To: basicstamps@yahoogroups.com
>Subject: [noparse][[/noparse]basicstamps] Ooooh, another exciting STAMP project!
>Date: Thu, 7 Jun 2001 12:34:0
>
>Here's the current STAMP task I'm faced with... any help appreciated.
>
>I am trying to build a device that will both monitor and regulate the
>temperature of a cylinder of water, holding somewhere between 2 and 6
>ounces. The temperature needs to stay at a constant setting of about
>100 degrees F. Sometimes, the cylinder will be emptied, and the device
>needs to be able to detect this as well. The power source will be AC
>from a wall socket, though I'd prefer it to be battery powered via
>some off-the-shelf variety of battery.
>
>Any thoughts on this? As usual, writing the software is not a problem
>for me, building the hardware is, and I'm a little unclear as to how
>to heat water using electricity, esp if it's supposed to be regulated.
>
>Thanks,
>-Chilton
>
>To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
>from the same email address that you subscribed with. Text in the Subject
>and Body of the message will be ignored.
>
>
>Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
_________________________________________________________________
Get your FREE download of MSN Explorer at http://explorer.msn.com
What you will need here is a closed loop control system. That means you have
a resistor (maybe some nichrome wire) to heat the water and a sensor (like a
thermistor or a thermocouple) to read the temperature.
Now in a perfect world, you'd turn power on to the heater until you hit your
target and then you'd turn it off. That doesn't really work though. The
reason is that real world systems have different types of response.
For example, water will act as a capacitor, storing heat. Your wire won't
cool immediately when the power goes off. So if you do what I said, you'll
probably overshoot the mark.
PID control is the classic control systems way of dealing with this problem.
The loop has three "gain" proportional, integral, and derivitive (PID).
P is what you normally think of. If the water is 1/10 degree off, you just
pass a little current through the resistor. If the water is 10 degrees off,
you push more current.
I is the integral term. Think of this as a little bit that keeps adding in
each time through the loop. This makes long term adjustments to the system.
D is derivitive -- a reaction to change. So as you get nearer the set point
temperature, the slope of the error reduces and this term reduces as well.
This reacts to short term glitches.
People who understand this well (which does not include me) can tune this
sort of thing to take into account dead lag and other pheonomena. For
example, since the water acts like a capacitor, you'll have to dump some
energy into it before anything really happens. Then you have too much
energy.
Remember, these gains can be fractional or even negative.
Some reading:
http://www.controleng.com/archives/1996/02/issues/na/02c152.htm
http://www.parallaxinc.com/downloads/Documentation/Educational%20Curriculum/
ic6.pdf
Sometimes this is all overkill and you can just turn your resistor on until
you get the temp you want and then turn it off. Be sure to build a little
hysterisis in at least (in other words, if your setpoint is 100 degrees +/-2
degrees, you might turn off at 101 and turn on at 99 so you don't just flip
on and off all the time.
In some cases proportional is enough, too.
Regards,
Al Williams
AWC
* 8 channels of PWM: http://www.al-williams.com/awce/pak5.htm
>
Original Message
> From: chilton@t... [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=NqEO5RVSxDphagQj1t4oBAGh0wGXKkuKwENX7GjDmuARXYYZ_NmbxMbTO5ghanN0kknoNZhzBw]chilton@t...[/url
> Sent: Thursday, June 07, 2001 12:00 PM
> To: basicstamps@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] Ooooh, another exciting STAMP project!
>
>
> Here's the current STAMP task I'm faced with... any help appreciated.
>
> I am trying to build a device that will both monitor and regulate the
> temperature of a cylinder of water, holding somewhere between 2 and 6
> ounces. The temperature needs to stay at a constant setting of about
> 100 degrees F. Sometimes, the cylinder will be emptied, and the device
> needs to be able to detect this as well. The power source will be AC
> from a wall socket, though I'd prefer it to be battery powered via
> some off-the-shelf variety of battery.
>
> Any thoughts on this? As usual, writing the software is not a problem
> for me, building the hardware is, and I'm a little unclear as to how
> to heat water using electricity, esp if it's supposed to be regulated.
>
> Thanks,
> -Chilton
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed with. Text in
> the Subject and Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
>I am trying to build a device that will both monitor and regulate the
>temperature of a cylinder of water, holding somewhere between 2 and 6
>ounces. The temperature needs to stay at a constant setting of about
>100 degrees F. Sometimes, the cylinder will be emptied, and the device
>needs to be able to detect this as well. The power source will be AC
>from a wall socket, though I'd prefer it to be battery powered via
>some off-the-shelf variety of battery.
>
>Any thoughts on this? As usual, writing the software is not a problem
>for me, building the hardware is, and I'm a little unclear as to how
>to heat water using electricity, esp if it's supposed to be regulated.
>
>Thanks,
>-Chilton
Check out the industrial control unit at
http://www.stampsinclass.com
It develops a temperature controller in a film can.
Driven from low voltage, a ceramic power resistor (e.g. XICON PRM5
from Mouser) can make a good heater for low temperatures like your
100 'F. Leads or the whole thing can be coated with plastic dip.
Don't allow it enough power to get dangerously hot. If the liquid
disappears, the whole response changes as it can heat up very fast.
Or you can have a separate water detector. If the heat loss is
great, then you will need a more substantial heater.
I have a water filled thermos bottle maintained at a 50'C for
calibrating temperature probes. Being a thermos, it takes hardly any
power to maintain the temperature.
-- best regards
Tracy Allen
electronically monitored ecosystems
http://www.emesystems.com
mailto:tracy@e...
You've had a couple of good suggestions on the heater (I used an AC beverage
heater like those used to make a cup
of instant coffee in a cup). I would also suggest you use a small pump to
circulate the water. This will give you a
nice even temperature throughout the fluid you are heating instead of a range.
An aquarium pump could work or a small
RC fuel pump.
Regards, Theron
> >
Original Message
> > From: chilton@t... [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=VrcnXpNUgRNsxW-BAGDTyKDUqM9F3n-I0jA1gU7hHU_SrcPVR4eB0NNV2rsXzEVBjSJ0AFCr2A]chilton@t...[/url
> > Sent: Thursday, June 07, 2001 12:00 PM
> > To: basicstamps@yahoogroups.com
> > Subject: [noparse][[/noparse]basicstamps] Ooooh, another exciting STAMP project!
> >
> >
> > Here's the current STAMP task I'm faced with... any help appreciated.
> >
> > I am trying to build a device that will both monitor and regulate the
> > temperature of a cylinder of water, holding somewhere between 2 and 6
> > ounces. The temperature needs to stay at a constant setting of about
> > 100 degrees F. Sometimes, the cylinder will be emptied, and the device
> > needs to be able to detect this as well. The power source will be AC
> > from a wall socket, though I'd prefer it to be battery powered via
> > some off-the-shelf variety of battery.
> >
> > Any thoughts on this? As usual, writing the software is not a problem
> > for me, building the hardware is, and I'm a little unclear as to how
> > to heat water using electricity, esp if it's supposed to be regulated.
> >
> > Thanks,
> > -Chilton
> >
> >