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testing a lm335 at 35 degrees

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cbiblis

New Member
I have a lm335 that i need to test at 35degees. i have the sensor in the fridge that is set for 35 degrees.These are analog sensors, which according to the data sheet output a voltage proportional to temperature. The calibration seems to be 10mV/degreeC. i need to know the voltage that the sensor is putting out. i have it hooked up to a thermo controller and the sensor is getting the proper voltage for operation.i have a multimeter. can some one tell me how to read the value of the sensor.
 
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ericgibbs

Well-Known Member
Most Helpful Member
I have a lm335 that i need to test at 35degees. i have the sensor in the fridge that is set for 35 degrees.These are analog sensors, which according to the data sheet output a voltage proportional to temperature. The calibration seems to be 10mV/degreeC. i need to know the voltage that the sensor is putting out. i have it hooked up to a thermo controller and the sensor is getting the proper voltage for operation.i have a multimeter. can some one tell me how to read the value of the sensor.

hi,
The LM335 is from -40C to +100Cdeg, you are quoting 'Fdegs'.
Convert the 35F to centigrade and should get 10mV/Cdeg.

What voltage does your DVM read.??
 

MrDEB

Well-Known Member
the lm335 is 10mv per kelvin not Celius

at 35 degrees Fahrenheit the voltage should be 2.74 volts.
 

cbiblis

New Member
OK then. i need to test the voltage of the lm335 at 1.6 centigrade. How would i go about testing the voltage with my multimeter? i don't know what you mean by dvm, however the circuit is 12v. i'm using a battery as a supply. When i test the power at the sensor connectors without the sensor connected i read 12v. is this what you are asking?
 

MrDEB

Well-Known Member
here is pic from data sheet

if in doubt look at data sheet
at 1.6c = 2.74 volts
 

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cbiblis

New Member
thanks deb. But just for the sake of argument, is there a way to test the sensor with a multimeter?
 
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MrDEB

Well-Known Member
use the volt setting on the multi meter

hopfully you have a digital volt meter.
just connect a battery to the lm335 and wire the lm335 as per data sheet.
I think maybe an ohm meter might work as well??
I recall seeing somethingon the data sheet about resistance but ??
 

Boncuk

New Member
The LM335 needs to be calibrated.

Measuring the output voltage at any given temperature the output error is unknown.

The output voltage of the LM335 might be 2.92 to 3.04V at 25deg/C, the LM335A has an output voltage between 2.95 to 3.01V.

For accurate calibration use a test chamber at 25deg/C with the DUT and a precise reference thermometer.

For least offset error use the LM135A/LM235A with a maximum output error of 20mV (2.97 to 2.99V).

Ideally the output voltage should be 2.74866V at 35deg/F.

For highest accuracy you might consider using the Sensirion SHT11 or SHT75 (combined humidity/temperature sensor), calibrated during manufacturing and fitted with a 16 bit resolution serial interface.

SHT11 and SHT75 are identical from design. The difference is the mounting method. The SHT11 needs a separate PCB with a 4-pin connector, while the SHT75 is already fitted with that connector.

Boncuk
 

Mr RB

Well-Known Member
The LM335 needs to be calibrated.

...

??? It comes standard at 10mV/'K and accuracy of +/- 1 degree.

If you want it more accurate than that you can calibrate it. For most temperature controllers etc +/- 1 degree is perfectly acceptable and it never needs calibrating.
 

Roff

Well-Known Member
Are you connecting a resistor in series between the battery and the LM335? If so, what value are you using?
 

Boncuk

New Member
??? It comes standard at 10mV/'K and accuracy of +/- 1 degree.

If you want it more accurate than that you can calibrate it. For most temperature controllers etc +/- 1 degree is perfectly acceptable and it never needs calibrating.

NO! It does not come standard at 10mV/K and and an accuracy of ±1 degree.
Just the 10mV/K is standard. The offset varies a lot.

So why does the OP want to measure the output voltage instead of calculating it according to your truth - which adds extra inaccuracy?

If you read the datasheet thoroughly you'll notice that the LM335 is accurate to ± 60mV (meaning ±6 degrees).

Reading posts only halfway and responding wrongly will create confusion!

Once again: The LM135A/235A have an offset of ±10mV of the standard value of 2.98V while the LM335 has an offset of ±60mV and the the LM335A still has one of ±30mV.

An accuracy of ±1 degree is not a measurement, but a rough estimate! Tests prove that humans consider a temperature change of 0.5deg/C either too hot or too cold!

When I posted the difference between LMxxx temperature sensors there was nothing personally involved in that.

You are trying to make it a personal discussion!

Watch it! I'm not in the mood to play or fool around!

Boncuk
 
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Sceadwian

Banned
Boncuk, I'm not sure how you took two lines of text to be a personal attack. Did you not take a nap today? =) cbiblis hasn't even mentioned word 1 of the intended use for the sensor in this thread so going off half cocked about accuracy is a bit premature.

cbiblis, a DVM means Digital Voltage Meter. IE a Multimeter. So yes you can test it. To calibrate simply get the sensor to a known temperature (this is actually the hard part) Read the voltage on output with a multimeter and that's your reference point for that temperature. You will obviously need a meter that can measure mv's accurately. Every 10mv's above or bellow that reference voltage will be 1 degree Celsius warmer or colder than the reference temperature. The calibration will be only as good as the reference thermometer and your multimeter's accuracy.

It would help at this point if you would clarify your intended use and operating range.
 
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Boncuk

New Member
Boncuk, I'm not sure how you took two lines of text to be a personal attack. Did you not take a nap today? =)

Hi Sceadwian,

I didn't take two lines of text to be a personal attack, but the two (too many) question marks preceeding the text. :mad:

No question that someone putting too many question marks in front of a sentence has no chance to survive in my company. :(

I guess we're here to help or get help. If the OP wants to measure the output of the sensor at a given temperature he must have a good reason for it.

Further I just repeated in short terms what everybody can read in the LM335 datasheet. I used it for a motorbyce handle heater circuit and you can bet the MCU has a software built in calibration routine. (works just comparing both sensor values (one known) and determining the offset).

No, I didn't have a nap today. We're going through the second f... hot season in Thailand (sun moves from North to South crossing Thailand at a 90deg zenith angle). Temperatures rise to 45deg/C at noon and that's not the time to take a nap.

Anyway, I feel fit and awake enough to read the poster's intentions.

Regards

Hans
 

MrDEB

Well-Known Member
Handle bar heater??

give me a break, your kidding I think.
maybe in the frozen arctic but the south pacific??
 

Vizier87

Active Member
It should indicate the average temperature of the air flow, what app do you have in mind.?

I was thinking of a concept of an anemometer. A reference temperature for the ambient and the external airflow temperature, and the difference between these two outputs should indicate airspeed, right?
 

Mr RB

Well-Known Member
I apologise for offending you Boncuk, that was NOT my intention.

I often use the ??? prefix to mean "huh?" and what I meant was as much "huh? I don't understand?" as it is "huh? are you sure you are right?". My implication was that there seemed to be a difference between what you believed and what I believed. It was NOT a personal attack. If I attack you it will be most obvious.

Now back to the difference of OPINION, you stated the LM335 needs to be calibrated. See my post #12 and the quote I was referring to. I think your statement is wrong. I use LM335A quite often and they are usually within 1'C accuracy. I don't care if the datasheet says 3'C because in my real world experience all the units I have used have been within 1'C and my experience tells me that they DON'T need to be recalibrated for most general uses like temperature control and/or displaying 'C with a display where the PIC adc only gives 0.5'C display resolution.

If someone needs greater than 1'C accuracy that falls under the special needs category; ie "CAN be recalibrated for better accuracy", not the global; "NEEDs to be recalibrated" category.
 

Boncuk

New Member
give me a break, your kidding I think.
maybe in the frozen arctic but the south pacific??

Questionmarks seem to be your hobby.

It might not be realized by you that I'm German, just happening to live in Thailand. Germany gets pretty cold during the winter time and riding a motorbyce at -25deg/C is no fun even with heavy gloves.

Therefore I designed the handle heaters which almost instantaneously increase heating power if the driver removes one hand from the handle. Of course both handles are heated independently.

Any more breaks you need?
 
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