Ask me questions about Sensors

Hi Jane,

i want to use a pressure sensor (MPX5100DP) and a mass flow sensor (AWM3300V).

Are these components ready to use or they need some kind of calibration? If so, how is it done?

F.

Hi,

Unfortunately the pressure sensors you mentioned does not belong to Panasonic so I'm not sure if it needs callibration or not.

Please visit our website below for our list of pressure sensors. Currently our flow sensors are under development.

Thanks

http://pewa.panasonic.com/components/built-in-sensors/pressure-sensors/

Dear Jane,

     I have recently bought a non contact IR tempereature sensor, TPD 1T 0214, a product manufactured by Excelitas. However, the output voltage yield by this component is too small (approx. less than mV). I have difficulty in amplifying the signal and has even tried to contact the supplier and Element14 to help me with this but still no response were given. It would be greatly appreciated if you could help me with this

That sensor is replaced by the TPS334 according to Excelitas.

If you Google for thermopile infrared sensor you get lots of hits - here's an early one that talks about amplifiers:

http://www.analog.com/en/content/using_thermopile_sensor_in_ir_digital_thermometers/fca.html

You don't say what you are trying to do or what your experience is, but unless you are prepared to learn a lot about low noise small signal amplifiers you might do better to buy a ready made thermometer.

MK

Dear Michael,

First of all, thanks for the information. I am currently a student and is trying to work out with a low budget mini project that wish to measure human fingertip temperature using non contact temperature sensor like TPS334 and obtained a temperature from its corresponding output voltage. The output voltage that i obtained is from leg 1 and leg 3 of tps334 without applying any voltage source to it. The output signal obtained from tps334 is quite small, which is around 0.02mV. I have previously tried to amplify the signal using voltage mode configuration (using op-amp LM741) or non inverting configuration but i still failed to get an amplified output. The amplified output did not change according to the variation of input when human finger is present and absense. I was wondering how the op-amp can work at such small input signal. Could you help me with this? Thanks.

If your signal is that small you may be doing something wrong.

Start by checking you have the right pins (the other two pins are the built in thermistor so should measure about 30k ohms at room temperature).

When you have the right pins use a decent DMM to measure the voltage.

Farnell sell a similar sensor GE ZTP-135S and it suggests you should be seeing about 2.5mV which should easily show up on a DMM.

Once you have the sensor working you can design an amplifier.

You mentioned an LM741 - this was a great op amp when it was designed in 1968 some 45 years ago - things have moved on - follow that link I gave you from AD and choose  a decent op amp.

You want low noise, low offset, RR (rail to rail) output, try LMP2021.

But make sure the sensor is working before youstart with the op amp.

Simulate the design before you try to build it.

Then, just out of interest because I don't mind helping, if you are a student shouldn't your tutor be helping out a bit ?

MK

Hi, you mentioned that the very low output signal is wrong, but referring to a catalog by Excelitas (http://www.excelitas.com/Pages/Product/Thermal-Infrared-Detectors.aspx) (at the right side of site, pg 10 of catalog) i thought the low output signal was right since at human temperature the output voltage is ~0.02mV and I have tried to test the built in thermistor as well which yield 30kohm at ambient. I have tried to find a similar op-amp as suggested by you and is able to find LM358 at my place here. However, the output voltage is still low and i was wondering is the problem occur due to leg 1 and 3. Should the leg 3 be grounded? Regarding my tutor, he gave me the title and that the end, as he mentioned that his way of teaching is to let the student explore. Since i have very little experience in these electronic, so i am now learning while exploring these analogue device.

Have you tried connecting a DMM to the sensor yet. I still think you should get more than 0.02mV - even the lowest sensitivty sensor on that graph would give you about 0.2mV.

The LM358 is only a slight improvement on the 741 - it's another jelly bean op amp with awful specs.

You need a decent amplifer to work with these small signals.

LM358 7uV/C temperature drift, LMP2021 0.02uV/C - thats 350 times better.

It matters because your signal (if your measurements are correct) is only 20uV and the drift of the LM358 could easily be greater than that as your circuit warms up.

Tell me what you see with the DMM (ie reading with no fingers, finger at sensing distance, finger at 2 X sening distance) and I'll see if I can suggets a circuit.

(What course are you studying ?)

MK

Below is the value i got;

with no finger = 0

with finger, 0.3cm above sensing window = 0.4mV

with finger, 0.7cm above sensing window = 0.2mV

with finger, 1.2cm above sensing window = 0.1mV

I have bought the op amp as suggested by you. I am taking telecommunication course and is currently in my second semester of my first year.  

Hello,

They are throwing you in at the deep end !

You haven't said where the signal goes after the amplifer but I'm assuming you will need to get it upo into the range 0 - 3V from the sensor's 0 - 0.4mV so you need  again of about 6000.

You will need more than one amplifier stage to do this !

To keep things really simple you could try cascading two of the circuits shown on page 15 of the LMP2021 data sheet. They give some component values and other information on subsequent pages.

You will need  a single 5V power supply.

Set the gain of each stage to 50 which will give you an output of 500mV with the finger at 0.7cm.

Limit your bandwidth to about 10Hz (so as to make sure that mains hum doesn't affect you to much).

Remember that the amplifiers need power supply decoupling capacitors.

Have fun.

MK