Wrong reading of transducer voltage

Using Arduino Sensors
1

Equipment: Arduino UNO 3, Adafruit SD shield

Hi,

This is my first Arduino project and I am bit confused with the results I am getting.
I want to read the voltage from a transducer that is powered by the Arduino.

The transducer output is connected to Analog Pin 2.
My code is pretty simple:

analogread(A2) x 5/1023

However the reading I have is very different from what my multimeter is giving me.

Multimeter: -0.29V
Arduino: 0.00V

Is there something wrong with the grounding maybe?

Note:

  • the Arduino is powered by laptop USB
  • the transducer is powered by Arduino 5V and step up transformer

Many thanks in advance for your help.

Best,

image
image1512×2016 1.25 MB

2

Google says " A transducer is a device that converts energy (electrical signals is a form of energy) from one form to another so that the desired characteristics of the input energy can be read at the output signal. Transducers are a vital first link in your measurement chain.".

You failed to identify what your transducer is and what it does.

3

An Arduino cannot read negative voltages.

Please post a link to the product page or data sheet of the mysterious "transducer", and a pic of a hand drawn circuit diagram, with all connections and components clearly labeled.

4

If that's a minus sign, the Arduino doesn't read negative voltages. (It can be damaged by negative voltages greater than -0.5V, or voltages greater than 5.5V).

This also means that it can't measure unbiased AC voltages (and you only "sample" the AC voltage for one instant every time you read).

MAYBE you can reverse the connections. But the mystery sensor probably shouldn't be putting-out negative voltage either.

5

Thanks all for the prompt reply - the negative voltage was the issue.
FYI the transducer is a directional current reader transforming a 0 - 50 A signal into a 0 - 10V signal.
Now I need to improve the stability of the reading, I am considering using a 1.1V reference and adding a capacitor.

6

How do you plan to measure that with a 5V Arduino?

7

Voltage divider - now probably down to 1.1V

8

The 1.1V reference is stable, but not calibrated and can be anywhere between about 1.0 and 1.2V. So for accurate results, you need to calibrate the measurement using a separate standard voltage reference (e.g. a decent multimeter).

9

Thanks for the tip.
So in my formula I should put the reading I get from a multimeter e.g. 1.15/1023?

10

You need to calibrate the entire setup, which includes the voltage divider.

For "one point calibration", multiply the value obtained by analogRead() with a scale factor that gives the correct result, when an accurately known voltage is applied to the voltage divider.

11

Got it - thanks

12

Your transducer states that 24Vdc is needed to power its internal electronics, I don't see such a supply.

13

I use 5V and step up (on the picture)

14

I don’t see any code in your publication. Just remember that analogRead() returns an integer value from 0 to 1023 corresponding to a 0-5V range. If the input voltage is below 1V, analogRead() will return an integer number between 0 and 204, and your above “code” will be something like
204 x 5 / 1023, which is zero.

Please post your code so we’ll all be better informed to provide help.

15

Do you have the required 24 Volts at the transducer?

How good are your ground connections between power and the transducer ground and the board ground?

I always "print" the raw counts when troubleshooting.