RCV420: Best Current Sense Amplifier for 4-20mA Current loop

Hi Mark,

I would like to know more about your system before we move forward with picking the best component.

1. What acceptable range of shunt resistance are you operating with? The RCV420 has an internal shunt resistor of 75 Ohms - is this within or near your range of resistance?
2. What supply voltages are available in your system?
3. What ADC specifications are you working with and is there a specific part you're using? (i.e sampling frequency, input voltage range, bit resolution)

Best,

Kevin

Hi Kevin,

Thanks for your prompt reply. My goal is to obtain the best accuracy because unfortunatly my O2 sensors gives a range of 4mA to 20mA for a signal between 0 and 1000ppm and I have to detect 1 ppm!!

I’m hesitating between two electronic solutions, one using your RCV420 circuit and the second an INA190 circuit. 

The attached file shows you the assembly with the RCV 420 and the calculation note with the INA190 ( gain +25)  by taking a Rsense resistance of 10 ohms and a sensor supply voltage of +24V, +5V for the INA190. 

I will use also the ADS1115, a 16-bit A/D converter coded with VREF= +5V, which gives a "theoretical resolution" of  5/65535 = +76,3µV equivalent to 0.015ppm. The reading frequency is low on the order of a few hertz.

What is your point of view?

Thanks for your help,

Best regards,

Marc,TiForum_ReplyMMorand_250624.pdf

Hi Marc,

Thank you for sharing your schematic and calculation notes. There are a couple of things I wanted to point out that might require consideration:

• The ADS1115 also has a built-in programmable gain amplifier (PGA) that requires a resolution to be chosen. I see in your notes that you plan to use the +/-6.144V FSR, which would give you a resolution of 187.5µV. This resolution would fit your 1 ppm threshold, but I thought to mention it again since it wasn't mentioned in the post. 
• You may need to consider a smaller tolerance percentage resistor. At 20mA of input current across the 10Ohm resistor with a 0.1% tolerance, the input voltage can vary by 200uV, which would nearly be enough to equate to 1ppm of difference (0.99ppm) after multiplying by the INA190 gain of 25.
• What is the resistor's temperature drift? Depending on your operating temperature range, the changes in resistance value over temperature can also introduce significant error.

Overall, based on the design parameters provided, a 1ppm detection threshold should be achievable with the selected device.

Best,

Kevin

Hi Kevin,

Thanks for your prompt reply.

I have not yet chosen the type of 10 ohm resistor 

Perhaps with a temperature drift parameter less or around 10ppm/°C and a tolerance of 0.1%?

See attached file10R_10ppm.pdf

Regards,

Marc,

Hi Marc,

It seems that the INA190 is better fit for your design over the RCV420, so I'll be moving this thread over from Precision Signal Conditioning (PSC) to Current Sensing to make sure that you receive the best support for your application! 

Best,

Kevin