Hi, i have a couple of questions.
1-)I want to control temperature of water which has a constant volume with 220VAC current and a heating element precisely (error should be betweeen 0.1-0.3 degree celsius). But i can't decided what should i use for controlling AC power. There are many many options like solid state relay, mosfet, triac etc. As far as i understand these options provides on/off control. I want to use PID control too.
Are there any other options for regulating AC power continously (not on/off like regulating current)?
2-)In addition, temperature range will be between room temperature and 45 celsius. So the heating element and 220VAC maybe too powerfull for this project.
Do you have any other suggestions for heating? (Actually i prefer less power and DC current for portability and security)
NOTE: Heating time is important. I have not much knowledge about electronics so please explain simply.
Thank you for your answers.
Have multiple heaters, one for startup, maybe one for maintaining.
You will need stirring?
Use SSR for AC.
Maybe need an alarm annunciator.
Temperature display.
Ambient temperature in the PID
But i can't decided what should i use for controlling AC power. There are many many options like solid state relay, mosfet, triac etc. As far as i understand these options provides on/off control. I want to use PID control too.
With a delay it's very difficult to design a stable continuously-variable feedback control system. There's always a delay in heating/cooling systems and virtually all heating/cooling systems use on/off control.
So the heating element and 220VAC maybe too powerfull for this project...
...NOTE: Heating time is important.
You can [u]calculate[/u] the amount of energy it takes to raise a known amount of water by 1 degree.
Thank you for your answers. Do you think an SSR and PID control is sufficient for reaching an error between 0.1-0.3 celsius? (most probably i will use a thermistor as sensor)
. Do you think an SSR and PID control is sufficient for reaching an error between 0.1-0.3 celsius?
1/10th of a degree shouldn't be a problem. But, if you have a bucket of water there could easily be a one degree difference between the water at at the top and the water at the bottom (or between one side and the other, etc.).
(most probably i will use a thermistor as sensor)
Thermistors are non-linear and I'm not sure if you can get the accuracy & resolution you are looking for. It may work, I just don't know.... You certainly will have to calibrate it with a good-accurate thermometer. An LM34 or LM35 is easy to use, stable, and reliable.
DVDdoug:
Thermistors are non-linear and I'm not sure if you can get the accuracy & resolution you are looking for. It
Unlikely
You can get IC'c that are accurate at 0 and 100 deg C but the measurement accuracy is generally poor over the range by as much as 5 %.
If its a fixed not variable temperature required they can work if you have a suitable calibration source such as a good thermometer.
If you need a variable set point i would suggest a platinum resistance sensor.
Pid can maintain .1 deg accuracy in a stirred 200 litre tank, i have done that.
Not sure about 1 litre, i think it could but you may have to take into account insulation and external temp.
okan26south:
controlling AC power. There are many many options like solid state relay, mosfet, triac etc. As far as i understand these options provides on/off control. I want to use PID control too.
An ssr with zero volt switching would probably be the easiest/cheapest.
Depending on how many cycles you let through a 1kw heater for instance could generate anything from 10 W to 1 kW per second assuming 50 HZ mains.
okan26south:
Hi, i have a couple of questions.
NOTE: Heating time is important. I have not much knowledge about electronics so please explain simply.
Thank you for your answers.
How is it important ?
Heat up time from cold?
Do you have continuous flow , in which case the mechanical arrangement could be important.
Boardburner2:
Depending on how many cycles you let through a 1kw heater for instance could generate anything from 10 W to 1 kW per second assuming 50 HZ mains.
A half cycle has a big DC bias, which if repeated with the same polarity will push lots of DC
back into the mains and unbalance it.
For temperature control of water you can afford much longer timescales for PWM, since water
has a large heat capacity. On-off switching on a 10s cycle (on zero crossings) might be a reasonable
compromise - so long as the heating element isn't too huge.
1 litre of water takes 420 joules to heat by 0.1degC, so a 50W heater will take about 10s to produce
that delta-T
If you want rapid heat-up consider two elements, a larger one for initial heat-up and the smaller
for temperature regulation.
Also for good temperature control you will need continual stiring.
