Monitoring 15 thermistors by computer

[amdx]

Hi All,
I have freezers that I'd like to monitor by computer display.
I can place a thermistor in each freezer and cable these to my computer.
I'm looking for how to get the data into the computer and a program to
display the temperatures
on the monitor. High temperature alarms would be a bonus.

Thanks, Mike

 

[Joerg]

Hint:
Multi-channel ADC.

Or single channel ADC plus two 74HC4051. Possibly you can also use the
sound card with an excitation frequency of a few kHz and measure the
amplitude with its input. Saves the ADC. Other than the 74HC4051 and
some jelly bean parts that would be almost free. But someone has to
write the software ...

Depending on what accuracy you need you might need to use four 74HC4051
in order to calculate out its Rdson, since sound cards have a fairly low
input impedance.

 

[K Ludger]

Hi All,
I have freezers that I'd like to monitor by computer display.
I can place a thermistor in each freezer and cable these to my computer.
I'm looking for how to get the data into the computer and a program to
display the temperatures
on the monitor. High temperature alarms would be a bonus.

Thanks, Mike

What about dallas 1 wire temp sensors, no analog interfacing required.

http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2815
google around there are quite a few examples on how to use them

 

[CheapscateDave]

Hi All,
 I have freezers that I'd like to monitor by computer display.
I can place a thermistor in each freezer and cable these to my computer.
I'm looking for how to get the data into the computer and a program to
display the temperatures
on the monitor. High temperature alarms would be a bonus.

                                   Thanks, Mike

Hi Mike,
I use this program with Dallas/Maxim hardware. It will do everything
you want including alarms.

http://www.elektroniikka.org/thermometer/

Dave

 

[hrh1818]

Hi All,
 I have freezers that I'd like to monitor by computer display.
I can place a thermistor in each freezer and cable these to my computer.
I'm looking for how to get the data into the computer and a program to
display the temperatures
on the monitor. High temperature alarms would be a bonus.

                                   Thanks, Mike

One thing the other two replies haven't mention is how to measure the
change in resistance with temperature of your thermistor. One method
is supply a constant current to the thermistor and then measure the
voltage drop across the thermistor. This method requires a constant
current supply for each thermistor. Depending upon your accuracy
requirements you may be able to measure the voltage drop at the power
supply. But if your accuracy requirements are high you will need to
run 4 wires to each thermistor,measure the voltage drop at the
thermistor and use an analog to digital converter with a differential
input. A second method is to connect the thermistor in Wheatstone
bridge configuration. With this method you need one constant voltage
power supply, 3 precision resistors for each thermistor and a
differnetial input analog to, digital converter.

I hope I have scared you away from using thermistors to measure
temperature. A much better approach is to use Maxim one wire
temperature sensors. See http://www.maxim-ic.com/products/1-wire/
The temperature range of one wire temperature sensors is -40 to 85
degrees Centigrade.

 

[Joerg]

One thing the other two replies haven't mention is how to measure the
change in resistance with temperature of your thermistor. One method
is supply a constant current to the thermistor and then measure the
voltage drop across the thermistor. This method requires a constant
current supply for each thermistor. Depending upon your accuracy
requirements you may be able to measure the voltage drop at the power
supply. But if your accuracy requirements are high you will need to
run 4 wires to each thermistor,measure the voltage drop at the
thermistor and use an analog to digital converter with a differential
input. A second method is to connect the thermistor in Wheatstone
bridge configuration. With this method you need one constant voltage
power supply, 3 precision resistors for each thermistor and a
differnetial input analog to, digital converter.

I hope I have scared you away from using thermistors to measure
temperature. A much better approach is to use Maxim one wire
temperature sensors. See http://www.maxim-ic.com/products/1-wire/
The temperature range of one wire temperature sensors is -40 to 85
degrees Centigrade.

Often you can get by with a simple trick: Use a known resistors in
series with each thermistor and either supply them all with a constant
voltage or measure that voltage. 15 thermistors leaves one mux channel
free to do that so Mike could save the 50c or so for a regulator circuit ;-)

Done it many times, works. Of course this is not going to yield super
scientific precision.

 

[amdx]

Hi All,
I have freezers that I'd like to monitor by computer display.
I can place a thermistor in each freezer and cable these to my computer.
I'm looking for how to get the data into the computer and a program to
display the temperatures
on the monitor. High temperature alarms would be a bonus.

Thanks, Mike

 

[amdx]

Thanks guys, I'll mull over these ideas and see if I can get something put
together.
Mike

 

[neon]

why thermistor not thermocouple. well anyhow if you finaly figure out how to read one then all you need is multiplexing for how many ch. you want.

 

[gravpoet]

  Thanks guys, I'll mull over these ideas and see if I can get something put
together.
                                                               Mike

Try this...
http://www.measurementcomputing.com...1681&mscssid=QLTMA4FPPA479MSM18P7HWJE45DMDP6F

 

[amdx]

Thanks guys, I'll mull over these ideas and see if I can get something put
together.
Mike

Try this...
http://www.measurementcomputing.com...1681&mscssid=QLTMA4FPPA479MSM18P7HWJE45DMDP6F

That's nice, but I'm looking for the $49.99 version if I can't find the
$24.99 version.
Mike

 

[hrh1818]

  Thanks guys, I'll mull over these ideas and see if I can get something put
together.
                                                               Mike

The following Web page has some good information that can help you
evaluate if the one wire route is suitable for your application.
http://www.maxim-ic.com/products/ibutton/software/tmex/index.cfm

Howard

 

[hrh1818]

  Thanks guys, I'll mull over these ideas and see if I can get something put
together.
                                                               Mike

Another approach is to use the Arduino open-source electronics
prototyping platform. See http://www.arduino.cc/ for an overview of
the Arduino platform. The item we are interested in is the Arduino
Duemilanove. See
http://arduino.cc/en/Main/ArduinoBoardDuemilanove This prototyping
platform has a microprocessor, 14 digital I/O pins, 6 analog input
pins, a 10 bit analog to digital converter, and connects to a PC with
a USB cable. The cable is used to download programs to the
microprocessor, send data to a PC and to supply DC power to the board.
Here is a link to a page that demonstrates how the Arduino platform
can be used to measure temperature with a thermistor.
http://www.reprap.org/bin/view/Main/Temperature_Sensor_1_1 Or for
one wire temperature sensors see:
http://www.arduino.cc/playground/Learning/OneWire
If you need more than 6 analog input channels analog multiplexer ICs
like the 4051 or MC14067can be used to increase the number of analog
inputs. One person used the MC14067 to increase the number of analog
input channels to 96.

But the biggest selling point is the Arduino Duemilanove. only costs
$35 plus shipping.

Howard

 

[amdx]

Hi All,
I have freezers that I'd like to monitor by computer display.
I can place a thermistor in each freezer and cable these to my computer.
I'm looking for how to get the data into the computer and a program to
display the temperatures
on the monitor. High temperature alarms would be a bonus.

Thanks, Mike

Hi Mike,
I use this program with Dallas/Maxim hardware. It will do everything
you want including alarms.

http://www.elektroniikka.org/thermometer/

Dave

Hi Dave,
I've dowloaded that program and the update and language pack.
I can't open the .lng file exgtension. What do I use?
I couldn't locate help file in the program.
Can you give me some guidance?
I want to see if I can set it up to do what I want, before I order hardware.
Thanks, Mike