thermistor?

J

Johan Wagener

Guest
I need to design a thermometer that will monitor air temperature. I
don't know which of the best is the following. What are the pros and
cons of these? Which is best for use as an air sensor?

thermistor, pyrometer, thermopile

I have to power the circuit and apply signal conditioning to display
the temperature at least 5m from the sensor.

What will the circuit basically consist off?

How can I implement the following?

sensitivity adjustment
offset adjustment

what measures can be taken to prevent readings getting corrupted by
magnetic/electromagnetic interferences?

I am stuck at deciding on which sensor to use? LM335? PT100?

Any help on this will be greatly appreaciated
 
"Johan Wagener" <johanwagener@webmail.co.za> wrote in message
news:c86a2c09.0403171026.28a07dc2@posting.google.com...
I need to design a thermometer that will monitor air temperature. I
don't know which of the best is the following. What are the pros and
cons of these? Which is best for use as an air sensor?

thermistor, pyrometer, thermopile
Click to expand...
Thermistors are simple, and easy to work with, and cheap.

If you need to know absolute temperatures, you'll get familiar with the
hart-steinhart equation.
Otherwise, temperature is proportional to resistance, though not linearly.

National Semi makes some temperature sensor chips that give you 10mV/degree
or something like that, which would probably be easier to use if you want to
know temperature in degrees.
 
Dave VanHorn wrote:


National Semi makes some temperature sensor chips that give you 10mV/degree
or something like that, which would probably be easier to use if you want to
know temperature in degrees.
Click to expand...
LM34 and LM35

I have used these and they are convenient.

MikeM
 
Johan Wagener wrote:

I need to design a thermometer that will monitor air temperature. I
don't know which of the best is the following. What are the pros and
cons of these? Which is best for use as an air sensor?

thermistor, pyrometer, thermopile

I have to power the circuit and apply signal conditioning to display
the temperature at least 5m from the sensor.

What will the circuit basically consist off?

How can I implement the following?

sensitivity adjustment
offset adjustment

what measures can be taken to prevent readings getting corrupted by
magnetic/electromagnetic interferences?

I am stuck at deciding on which sensor to use? LM335? PT100?

Any help on this will be greatly appreaciated
Click to expand...
First off, I bought an indoor/outdoor thermometer from radio shaft for
ten bucks, and it has an internal sensor and a remote one on a lead
that's a few meters long. It's still running, maybe 5 or more years,
off a couple button cells inside.

But you can make a thermometer with a diode junction for the sensor.
Here's the schematic of another one that uses a 1k thermistor. You can
modify it for other values. The shunt regulator is very wasteful of
battery current, but since it is used only a few seconds a day, the
battery should last for years. You could also run it off four 1.5V
cells if R8 is reduced.


54. Remote Thermometer
Electronic projects 1981 P. 41
(Must be viewewd with Courier font)


+---(/\/\/\)----+
| TH1 |
| 1K @ 25 deg |
outdoors | |
------------------ | ------------- | ------
indoors | |
| |
+--/\/\/\-----+ |
| R2 1.8k | |
| | |
| \ |
| /<-+ |
| R4 \ | |
| 10k / | |
| trimmer | | |
| +--+ |
| | |
| \ |
+---+ R5 / +-------+
| | 12k \ |
| === / |
| GND | |
| +----------+ |
| M1 | + | |
| ,-----------, | |
| | 0 -100 ua | | + |
| | \ | / | --- C1 |
| | o | --- 47 uF |
| '-----------' | |
| | - | R6 |
| +----------+ 5k trim |
| R3 | R7 +----+ |
| 1.8k | 3.9k V | |
+---/\/\/\----+---/\/\/\--/\/\/\-+----+
| |
| \ D1 1N746A 3.3V Zener |
+------->|----------------------------+
| \ |
| SW1 P.B |
| / R8 820 |
+----o - + o----o/ o----/\/\/\----+
BT1 9V
(and batt holder/clips)
 
"Johan Wagener" <johanwagener@webmail.co.za> wrote in message
news:c86a2c09.0403171026.28a07dc2@posting.google.com...
I need to design a thermometer that will monitor air temperature. I
don't know which of the best is the following. What are the pros and
cons of these? Which is best for use as an air sensor?

thermistor, pyrometer, thermopile
Click to expand...
RTD's are very accurate for the range of temperature you are
measuring.




I have to power the circuit and apply signal conditioning to display
the temperature at least 5m from the sensor.

What will the circuit basically consist off?

How can I implement the following?

sensitivity adjustment
offset adjustment

what measures can be taken to prevent readings getting corrupted by
magnetic/electromagnetic interferences?

I am stuck at deciding on which sensor to use? LM335? PT100?

Any help on this will be greatly appreaciated
Click to expand...
 
"Walter Harley" <walterh@cafewalterNOSPAM.com> wrote in message news:<c3arlu$scm$0@216.39.172.65>...
"Johan Wagener" <johanwagener@webmail.co.za> wrote in message
news:c86a2c09.0403171026.28a07dc2@posting.google.com...
I need to design a thermometer that will monitor air temperature. I
don't know which of the best is the following.

What temperature range? How precise?
Click to expand...


Zero Degrees Celcius to 50 Degrees Celcius


Up to a degree precision
 
On 17 Mar 2004 10:26:30 -0800, johanwagener@webmail.co.za (Johan
Wagener) wrote:

I need to design a thermometer that will monitor air temperature. I
don't know which of the best is the following. What are the pros and
cons of these? Which is best for use as an air sensor?

thermistor, pyrometer, thermopile

I have to power the circuit and apply signal conditioning to display
the temperature at least 5m from the sensor.

What will the circuit basically consist off?

As others have noted, there are dedicated chips.
Click to expand...
But the most common, linear, and accurate sensor over
the range from near-absolute-zero to well over 100C is
an ordinary junction diode, or a diode-connected transistor.

To use one, you just measure the forward "resistance"
with the resistance range on a normal DMM. You will
need to calibrate it by reading an ice bath and a
boiling water bath, but it's perfectly linear after that.
(As opposed to thermistors, which are simple to
wire up by wildly non-linear)

How can I implement the following?

sensitivity adjustment
offset adjustment
Click to expand...
If you build your own current source and measure the
drop across the diode, you can have complete control
over these in the measuring circuit. But if you are going
to be trying to build a temperature-compensated current
source, then you would probably be better off using the
dedicated chip.
what measures can be taken to prevent readings getting corrupted by
magnetic/electromagnetic interferences?

I am stuck at deciding on which sensor to use? LM335? PT100?

Any help on this will be greatly appreaciated
Click to expand...


Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
 
On 18 Mar 2004 05:54:06 -0800, the renowned johanwagener@webmail.co.za
(Johan Wagener) wrote:

"Walter Harley" <walterh@cafewalterNOSPAM.com> wrote in message news:<c3arlu$scm$0@216.39.172.65>...
"Johan Wagener" <johanwagener@webmail.co.za> wrote in message
news:c86a2c09.0403171026.28a07dc2@posting.google.com...
I need to design a thermometer that will monitor air temperature. I
don't know which of the best is the following.

What temperature range? How precise?

Zero Degrees Celcius to 50 Degrees Celcius


Up to a degree precision
Click to expand...
Thermistors and proprietary base-metal RTDs are popular, cheap and
provide high initial accuracy that around 20-25°C and lower accuracy
at the extremes, which is fine for HVAC-type applications.
Precious-metal RTDs can provide the best overall accuracy and long
term stability. You can also look at IC sensors. Thermocouples are not
appropriate unless there is something you're not telling us about the
situation (need millisecond response times? ;-) )

Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
 
In article <q8bj50ttcg6n7c9dd3sm3klhdhqtuevqnb@4ax.com>, Spehro Pefhany
<speffSNIP@interlogDOTyou.knowwhat> writes
Thermocouples are not
appropriate unless there is something you're not telling us about the
situation (need millisecond response times? ;-) )
Another family of IC temp sensors provides 1uA/degK
Click to expand...
AD590 was the original AD part they also now supply plastic encapsulated
..
Accuracy is food o/p is linear and as its constant currrent theres no
problem due to long wires.

--
ddwyer
 
Don't know if you want to go to the trouble but I have been playing with a
2-wire serial that has built in temp measure as well as trip point interrupt
support. TCN75 has a -55C to +125 range at 2 degree and 0.5 degree over a
smaller range. Direct digital readout via 2-wire serial
interface.
http://www.microchip.com/1010/pline/analog/anicateg/thermal/tempsens/serial/tc
106xx/tcn75/index.htm

They also have other temp measure devices analog/digital and serial
out:
http://www.microchip.com/1010/pline/analog/anicateg/thermal/tempsens/index.htm


They have free samples available through the web site ;-)

(I have no connection with the company.)


On Thu, 18 Mar 2004 13:56:05 GMT, Bob Masta wrote:

On 17 Mar 2004 10:26:30 -0800, johanwagener@webmail.co.za (Johan
Wagener) wrote:

I need to design a thermometer that will monitor air temperature. I
don't know which of the best is the following. What are the pros and
cons of these? Which is best for use as an air sensor?

thermistor, pyrometer, thermopile

I have to power the circuit and apply signal conditioning to display
the temperature at least 5m from the sensor.

What will the circuit basically consist off?

As others have noted, there are dedicated chips.
But the most common, linear, and accurate sensor over
the range from near-absolute-zero to well over 100C is
an ordinary junction diode, or a diode-connected transistor.

To use one, you just measure the forward "resistance"
with the resistance range on a normal DMM. You will
need to calibrate it by reading an ice bath and a
boiling water bath, but it's perfectly linear after that.
(As opposed to thermistors, which are simple to
wire up by wildly non-linear)

How can I implement the following?

sensitivity adjustment
offset adjustment

If you build your own current source and measure the
drop across the diode, you can have complete control
over these in the measuring circuit. But if you are going
to be trying to build a temperature-compensated current
source, then you would probably be better off using the
dedicated chip.

what measures can be taken to prevent readings getting corrupted by
magnetic/electromagnetic interferences?

I am stuck at deciding on which sensor to use? LM335? PT100?

Any help on this will be greatly appreaciated



Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Click to expand...
 
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