Amplifier for sensor signal

Hi all,

I'm working on a project that utilizes a sensor that requires no power supply of its own but
produces current upon reacting to the active material, the produced current requires amplification to make it readable using external data collection equipment (basically the Arduino).

Now according to the datasheet, the specifications of the amplifier are described as below:
Feed output into an I/V amp. A good quality low noise op-amp is needed, and a dual supply (+ and -) is essential

I tried searching for amplifiers with these specifications but I don't seem to understand what's going on, most of these amps are converting from 5v to 24v for example, that won't work on Arduino am I right? and what does I/V mean?

I just need a tip from an expert in the field of how am I supposed to choose the right amp with only this given info, the datasheet didn't mention other info

Anyway I will attach it BA-R-Sensor-Datasheet.pdf (705.4 KB)

Thanks

See "Application Circuit" in the data sheet:
The reference circuit above is available pre-built from Dart Sensors for development purposes.

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I saw the picture of the pre-built circuit on their website, but I'm confused, can the Amplifier Output be connected to Arduino? what kind of connection is that?

Connect the output to an analog input. The voltage range is within the 5V supply. Adjust the amplification so that the signal is not clipped at the supply limits.

It does, doesn't it? The application circuit on page 5 seems pretty clear to me. Did you try it?

The OPA335 is likely your best choice. It has very high gain and very low offset voltage. The offset voltage is the difference between IN+ and IN- it should ideally be Zero. Non Zero offset will result in some error in your output.

An amplifier can only output a voltage equal to the power supply. So if you are supplying the sensor with 5V and your Arduino is 5V then there will NEVER be an amplifier output that could damage the Arduino.

The circuit show does not require + and - power.
The LM285 is a 1.2Volt reference. The way its connected the output with zero current from the sensor will be 1.2v as the sensor supplies current due to exposure to Ethanol the output of the amplifier rises above 1.2v

It's likely a BNC jack.

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There is nothing really special about BNC connectors. They are designed to be used with shielded wire, similar to cable TV wire but much smaller. But other than that, they are just another 2 wire connector.

Except that one wire is dedicated to the shielding (GND). It becomes dangerous as soon as some other grounded sheet of metal comes in contact with the BNC housing.

I doubt that will happen with an Arduino. And they've been doing it for decades on oscilloscopes, function generators and counters.

This sensor uses a virtual ground, certainly different from protective ground.

Is that controlled by the "Ground Reference Switch" on the sensor input board shown above?

Except that the manufacturer's recommended application circuit uses a unipolar 5V power supply.

Capture

I agree but I wouldn't call this a virtual ground, I would call it a bias or offset. The opamp is still connected to common.

Exactly :slight_smile:

This circuit is a pretty standard amplifier. The only change would be to try to change the J-Fet to a MosFet. And how it is drawn there is no button to zero the sensor.

I would try to operate Q1 (hopefully a MosFet) with the Arduino so no button is needed. It would require a MosFet with a low gate voltage requirement, maybe 2.5 or 3.0 V

Essential is the outer contact of the BNC connector of the sensor. It is kept at the reference voltage or however you call it, not at the GND of the remaining circuit.

That's why a JFET is used here. In unpowerd state it shorts the sensor, and it is turned off when Vcc is applied to its gate.

I would not design it that way, I would use the 5v ground for the connector. Or have a 2nd amplifier buffer the 1.20 bias.

The JFET I'll agree. One would have to find a device with extremely low leakage when biased off.

A BNC connector is inappropriate for that sensor. None of its pins should be subject to inadvertent environmental contact.

I'm sorry, I'm just not getting your concern :confused:

I have bench equipment made by leading mfg that has BNC connectors. I has a portable Fluke scope with BNC connectors. What do you see as different on this device?

Is this discussion informed by the schematic of the actual evaluation board, vs. the application circuit shown in the data sheet?