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| 4-20mA Loop powered application? |
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| FlimFlam89:
Hello everyone! I’m new here so please bear with me :) I’m working on a project for school and I though that it was done, but oy boy was I wrong. The project is to interface with a 4-20mA pressure sensor and read out the data to a screen. All of this should be loop powered. The micro controller and screen draw 3.5mA - 4mA at 3.3V (~0.5mA at 24V) so it’s not too much. The sensor I’m interfacing with is rated down to 8V. When I hook everything up individually it all works, I can read the mA signal from the sensor both with the multi meter and the ADC of the micro controller but as soon as I hook them up together only the microcontroller works. And the voltage at the sensor is at ~2.5V. What is going on? The schematic below is of the DC-DC and the measuring of the current. Thanks in advance for any help, its greatly appreciated! *EDIT* Added attached image of schematic |
| Zero999:
--- Quote from: FlimFlam89 on November 09, 2018, 08:56:39 am ---Hello everyone! I’m new here so please bear with me :) I’m working on a project for school and I though that it was done, but oy boy was I wrong. The project is to interface with a 4-20mA pressure sensor and read out the data to a screen. All of this should be loop powered. The micro controller and screen draw 3.5mA - 4mA at 3.3V (~0.5mA at 24V) so it’s not too much. The sensor I’m interfacing with is rated down to 8V. When I hook everything up individually it all works, I can read the mA signal from the sensor both with the multi meter and the ADC of the micro controller but as soon as I hook them up together only the microcontroller works. And the voltage at the sensor is at ~2.5V. What is going on? The schematic below is of the DC-DC and the measuring of the current. Thanks in advance for any help, its greatly appreciated! --- End quote --- I can't see the schematic. Please upload it here as an attachment, rather than on an external hosting site. |
| Sudo_apt-get_install_yum:
Here you go! You can right click it and, check source image and save/open it! Oops, forgot to add my comment :-[ Have you checked the grounding between the measuring circuit and the regulator? |
| Zero999:
It isn't very clear. Where's the MCU in the circuit? Draw the whole circuit, connected together, including the MCU and sensor. Ensure you make it crystal clear which part is which. It sounds like a grounding problem. |
| FlimFlam89:
--- Quote from: Hero999 on November 09, 2018, 09:26:50 pm ---It isn't very clear. Where's the MCU in the circuit? Draw the whole circuit, connected together, including the MCU and sensor. Ensure you make it crystal clear which part is which. It sounds like a grounding problem. --- End quote --- Yeah it might be a grounding problem. Could it be that the DC-DC converter in the sensor and the DC-DC converter in my design are "fighting" over the power and resulting in a voltage drop? Like why solar power circuits use a MPPT to regulate the power while not dropping the voltage like it does? |
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