help with the flow sensor FS5

Hi Leonel,

A reference circuit is included in the data sheet:

http://www.farnell.com/datasheets/484569.pdf

You may need to reduce or offset the output voltage. Here is a link to an example:

http://dl.dropboxusercontent.com/u/7549930/aaSchematic2-diffAmp.png

and a discussion:

output - arduino thermal anemometer - Electrical Engineering Stack Exchange

If you cannot build it, you might be able to use the evaluation module from Farnel:

160.00001 - IST INNOVATIVE SENSOR TECHNOLOGY - EVALUATION BOARD, FOR FS5 FLOW | Farnell UK

http://www.farnell.com/datasheets/1702754.pdf

Doug

hi Doug

Thanks for your response.

I saw the 2nd link in your response.I can  see circuit diagram its exactly something like that that am looking for but have a concern:

Its written sensor is it the FS5? and see heater as a block do need to buy a heater also? or its just the name of that leg of the sensor.

Please be sore explicite please

Waiting to hear from you.

Leonel

Hi Leonel,

The sensor includes the heater (Rs is the Sensor Resistance and RH is the heater resistance in the circuit - both of these resistors are stuck together as part of the sensor you have). One wire goes to the heater, one wire goes to the sense resistor and one wire is ground - internally connected to the other end of both resistors.

The circuit uses feedback from the sensor resistance to keep the heater at a constant temperature. The output of the circuit indicates how much voltage is needed to keep the heater at this temperature. As more mass flow takes heat away from the sensor, more voltage is needed to maintain the same temperature, so the output goes up as the mass flow increases.

Doug

Hi ,thank you so  much for your help.

Can you advise me on an altenative op amp as I cant find the LT1635  on RScomponent who our supplier here..

I wanted to supply my circuit with a small battery so I am wondering if I can't use 9V instead of that 12V.

In final have you build this circuit and it work 100%?

Thank you

Leonel

Hi ,thank you so  much for your help.

Can you advise me on an altenative op amp as I cant find the LT1635  on RScomponent who our supplier here..

I wanted to supply my circuit with a small battery so I am wondering if I can't use 9V instead of that 12V.

In final have you build this circuit and it work 100%?

Thank you

Leonel

Hi,

You could use a TLV271 (or a TLV272 which could replace both op-amps).

I don't know if 9 v is sufficient to supply the heater in this circuit, you may need to reduce R3 and R4.

I have not tried it...

hi Doug

Thanks for your response.

I try the circuit as you sent me but with no success.

Can you suggest an alternative circuit or which 12 volt battery i should use.maybe the 12 volt battery doesn't have enough current to heat up the sensor?

please can you connect me with somebody who have use the sensor before

Big thank you again

Hi,

When you connect it up, what voltage is on each pin of the transistor?

And each pin of each op-amp?

hi,sorry for the late response but apparently i am using the FS1 not FS5 can i use the same circuit. when i look at the datasheet of the FS1 there is a circuit on it different to the FS5. But on that circuit those resistors doesn't have value.

please help

leonel

The FS5 circuit should work fine for the FS1 sensor.

With a 12 V supply, the heater won't draw more than 120 mA, so any battery should be adequate.

If you measure all the voltages on the transistor and op-amp, we could help diagnose the issue.

hi,

here are the measurement on the voltage on the transistor : pin1 and pin2 = 0.6Vdc

on the oscilloscope i can see a waveform that its moving as i change the flow of the gas that i am sending to the sensor. but i have to reduce the volt per division to the smaller one to see that change.

I don't know if that its just noise or its the signal that i am suposse to see and i have to filter it.

Please guide me

leonel

The signal should not change quickly - if it is changing rapidly, then it is most likely noise.

The base of the transistor, which is connected to the output of the op-amp, should be  about .7 volts higher than the transistor emitter, which is connected to the resistor bridge.

It looks like the emitter voltage should vary between about 5 volts and 7.5 volts depending on the flow rate (temperature).

From your description of the voltages, it sounds like the voltage at the + input of the op-amp is too low. check to see that all resistors have the correct values and that the sensor and heater pins have not been reversed.

What are the voltages on the input and output pins of the first op-amp?

Referrng to FS5A flo sensor i have followng queries

1) i fitted fs5A flow sensor in a 12.5mm pipe(inner diameter) 6 feet in length.i opened valve and air flow started flowng through pipe.i read 6 volts at output of cicuit (evaluation board circuit). Now from this 6 volt at at output how can i calculate air velocity at 25 C temperature? Any relation?

2) secndly using king's law what is value of  "k" in that kings law with units

Anyone help me please i will be grateful

Referrng to FS5A flo sensor i have followng queries

1) i fitted fs5A flow sensor in a 12.5mm pipe(inner diameter) 6 feet in length.i opened valve and air flow started flowng through pipe.i read 6 volts at output of cicuit (evaluation board circuit). Now from this 6 volt at at output how can i calculate air velocity at 25 C temperature? Any relation?

2) secndly using king's law what is value of  "k" in that kings law with units

Anyone help me please i will be grateful

Dear Douglas,

In 5 pin opamp, what is the part number of it?

Why 2 pins are not connected which is used for operations?

Your early reply highly appreciated