AD3 Voltmeter: 5V range shows lover value than 50V range

[rcross]

Setup:

- power supply CH1 - set to 3.000V

- voltmeter CH1 - set to 5V range, offset 0, atten X1

- V+ connected to 1+

Result:

Voltmeter reads 2.6482V not changing.

When voltmeter range is set to 50V, it reads 3.008V occasionally flipping to 3.010V, which is expected behavior.

Why 5V range behaves this way? is 5V range really -2.5V:2.5V, so 3.0V is overvoltage?

[JColvin]

Hi @rcross,

Quote

Why 5V range behaves this way? is 5V range really -2.5V:2.5V, so 3.0V is overvoltage?

This is correct. The 5 V range is +/- 2.5 V as per the Analog Discovery 3 Specifications, https://digilent.com/reference/test-and-measurement/analog-discovery-3/specifications#analog_input_channels, so applying a 3 V signal is outside of that range.

You can apply an offset of -2 V (to shift the range down by 2 V, so the 5 V range is instead -0.5 V to 4.5 V), and then accurately measure the 3 V signal with the low-range measurement.

You can also measure the same 3 V signal on the Scope instrument by setting the offset to -2 V, the range to 500 mV/div (the largest voltage division that maintains the low range setting for better resolution), and click on the Measurements tab to add a defined measurement, such as the Average voltage value of the visible data on the screen for Channel 1 (or whichever channel you are measuring).

Let me know if you have any questions.

Thanks,
JColvin