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.??

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at 35 degrees Fahrenheit the voltage should be 2.74 volts.

 

Speaking of LM35, does the output changes with airflow?

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

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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?

 

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

Attached Thumbnails

 

 

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

 

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 ??

 

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

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it's dynamic resistance.

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??? 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.

 

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

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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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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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