With a few exceptions, nearly all sensors require some sort of power source to work. This is why the MonoDAQ-U-X comes with a channel capable of supplying power to your sensors or other low power electronics.
The MonoDAQ-U-X is capable of supplying up to:
- 24 V max voltage or
- 200 mA max current or
- 1 W total power
Which is enough to power multiple sensors. For example, eight PT100 can be connected at the same time. You can even connect a couple of 4-20 mA sensors without the need for an external power supply
To use the excitation or the power supply simply select either of them from the PWR pin drop-down menu:
The excitation mode is intended to supply a precise constant voltage.
In this mode, the MonoDAQ-U-X can supply voltages of either 2, 3.3, 5, 10 or 24 V. The advantage is that these fixed voltages have a very low noise of less than 1 μV RMS.
It is ideal for sensors where the measurement error depends on how clean the excitation voltage is. Strain gauges or resistive temperature sensors will benefit from the low noise of the excitation mode.
In case you want to know more about connecting RTDs to the MonoDAQ-U-X we have an entire manual entry dedicated to the topic.
The power supply mode can supply any voltage in the 1.5 V to 24 V range. The drawback is that the noise is higher. The power supply mode will supply a voltage with less than 1 mV noise.
It should be used whenever connecting a sensor that needs a specific voltage not achievable with the excitation mode. It also often comes in handy when testing components or just as a convenient and portable mini power supply.
Another advantage is the ability to manually adjust the voltage at any time. Even while measurement is taking place! Add an “input control” widget to the measure screen and adjust the output voltage in real-time.
Better yet instead of changing the voltage manually, you can set up a math channel that will drive the output voltage for you. Right-click on any of the column headers in the MonoDAQ plugin and select “edit columns”. Make sure that there is a checkmark next to the “source channel” option.
This opens up many possibilities of using the U-X as a control device or perhaps doing a measurement while doing some sort of voltage sweep. The limitation being that the voltage can only be updated fairly slowly. No matter how fast the driving signal the power supply voltage update rate will always be updated once per second.
Driving the output with math – example
A creative example to demonstrate the versatility of using a math channel to drive the voltage output is creating an electronic load. In other words, we can create a closed-loop control system.
Let’s say we want to use the load to discharge a battery at a constant current. We can use a linear MOSFET as an adjustable resistor. Then we use a shunt to measure the current flowing through the MOSFET. We use that current as an input to a PID controller (which can be found in math) and. Finally, we have the PID controller output to drive the gate of the linear MOSFET. This way the MonoDAQ-U-X will continually adjust the MOSFETs gate voltage to ensure the current we have set in the software is always flowing through the system.
Watch the video where we show off this exact application:
Measuring the output
Another very useful configuration to get familiar with is adding the internal current measuring resistors to the current loop when powering electronics. This can be used with either the excitation or power supply modes.
The GND pin already measures current by itself however it is intended as a rough estimate, not a high precision measurement.
Let’s say we want to use the MonoDAQ-U-X to measure the power draw of a microcontroller. The U-X’s EXC pin is connected to the microcontroller’s VCC pin. Instead of connecting microcontroller GND directly we first pass it through the internal resistor between CUR+ and CUR-. This configuration is shown below:
Now both the current and voltage are being measured precisely. This enables us to accurately calculate the power draw of the microcontroller.
If you are feeling fancy you could even connect some of the unused pins of the microcontroller to the MonoDAQ-U-X as digital inputs. Doing this would enable you to communicate what state the microcontroller is into the U-X. For example, make the microcontroller pull a pin high whenever it’s is doing some specific operation. This could be used to get a great insight into exactly when the microcontroller is most power-hungry.
If you need a refresher in U-X digital inputs read the manual entry on the topic.
In any case, adding a precise current sensing ability to the loop opens many possibilities of using the U-X as a smart precision power supply.