Wiki source code of MPS-2

Last modified by Michael Sibayan on 2022/05/03 16:48

author	version	line-number	content
		1	= Overview =
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		3	[[Decagon MPS-2 (Manufacturers webpage)>>url:http://www.decagon.com/products/soils/water-potential/mps-2-water-potential-temperature/\|\|rel="__blank"]]
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		5	This sensor communicates digitally via the SDI-12 protocol. [[http:~~/~~/www.sdi-12.org/>>url:http://www.sdi-12.org/]]
		6	The cRIO in Panel 02 contains an NI-9403 high speed digital I/O module. The FPGA on the cRIO is programmed with a custom SDI-12 communications emulator. The module is capable of communicating with approximately 26 of the 32 digital buses simultaneously, this limit is aparently a hardware issue related to the impedance of the SDI-12 sensor network (basically the current draw to communicate with all those sensors is more than the module can provide). To combat this problem, the SDI-12 network is polled in two parts - all 5TM sensors, then all MPS-2 sensors.
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		8	The digital signal, when decoded, forms a simple ASCII text string which identifies the sensor address, the matric potential, and the temperature in degrees Celsius. An example output string is "B-352+25.6" - this shows sensor address "B", potential of "-352" kPa, and temperature "25.6" Celsius.
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		10	The MPS-2 terminates to a [[custom junction board designed by Aztera>>doc:LEO.AzteraBOB]] (http:~/~/www.aztera.com/). The board provides a many-to-one junction for power, ground, and signal buses which allows for 32 SDI-12 sensors to be connected to a single signal bus.
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		12	= Calculation Notes =
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		14	{{display reference="MPS2_CalculationNotes"/}}
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		16	= Wiring Diagram =
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		18	[[image:MPS2_Wiring_Schematic.png\|\|style="display: block; margin-left: auto; margin-right: auto; width="]]