My Ametek 955 gives output in 0-10V. I made a simple voltage divider to get it halved before I sent it to the analog input on the arduino. When I test the divider circuit before attaching the output lead to the arduino, I find the output from the transducer now maxes out at 9.36V instead of 10V as before. The circuit does its job, and reduces this by half. However, when I connect the divider output lead to the arduino, the signal from the transducer is further reduced to 8V max, and the voltage between the A4 analog pin where I've attached the divider output and ground is 2.25V. While the raw output is still linear, the voltage across A4 is not. What gives?
I am powering the transducer directly through the 12V lead from the power socket, which i have isolated from the rest of the board. The arduino is then powered by the usb socket.
When asking hardware questions, a schematic is required. Written descriptions are always more ambiguous than a drawing. Hand drawn, photographed and posted is fine. Include all pin names/numbers, components, their part numbers and/or values and power supplies.
The Arduino and the voltage to be measured must share a Ground.
What resistors are you using for your voltage divider? If the values are too low they will cause a drag on the voltage source. Something around 10k would be good.
I have not modifed the ground of the 12V socket, and have connected the transducer ground to the board. My resistors are only 330ohms, so I can fix that. Will that fix the linearity?
The 2 10K resistors for the simple voltage divider restored the max voltage signal from the transducer, but the voltage on the output lead of the divider is not half, but more like 15%, and not linear.
The data sheet does not provide any information about the output impedance of the sensor, which is needed.
However, if you are claiming that full voltage appears where the "upper" 10K resistor is connected to "signal" and only about 15% of that voltage appears at A5, then one or the other, or both of those resistors is not 10K.
They both came out of the same bag, and have the same color code. The same problem of not getting a halved voltage output and nonlinearity occurred when I had (2) 330ohm resistors instead. That isn't the problem, unfortunately.
I'm not sure what you mean, but I just checked it by maxing out the travel on the transducer and getting 10V before the divider, but not 5V after it. I checked linearity by moving sensor 2" at a time and checking the output from the divider.
Is the Arduino powered up? If not, A5 is nearly a dead short to ground.
In any case, the A5 input is severely loading the voltage divider. It may have been destroyed by earlier experiments.
As a safety precaution it is usually a good idea to put a 1K to 10K resistor in series with analog inputs, to reduce excessive current draw and consequent destruction, in case of applying an overvoltage.
