Scribd
Upload
106 views9 pages

Building A Resistive Wave Probe: Massachusetts Institute of Technology 12.097

The document describes how to build a resistive wave probe using an electronics assembly with a data logger, microcontroller, power amplifier, and level shifter connected to batteries. It discusses the concepts of resistance, conductivity, and resistivity in seawater and calculates the equivalent resistance of a sample probe configuration. The document also includes an electronics schematic and guidelines for testing and deploying the probe, including logging data with the TT8 microcontroller.

Uploaded by

Ankit Ghosh
Copyright
© Attribution Non-Commercial (BY-NC)
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
106 views9 pages

Building A Resistive Wave Probe: Massachusetts Institute of Technology 12.097

The document describes how to build a resistive wave probe using an electronics assembly with a data logger, microcontroller, power amplifier, and level shifter connected to batteries. It discusses the concepts of resistance, conductivity, and resistivity in seawater and calculates the equivalent resistance of a sample probe configuration. The document also includes an electronics schematic and guidelines for testing and deploying the probe, including logging data with the TT8 microcontroller.

Uploaded by

Ankit Ghosh
Copyright
© Attribution Non-Commercial (BY-NC)
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
You are on page 1/ 9

Building a Resistive Wave Probe

Massachusetts Institute of Technology 12.097

Start logging Computer Download data

Electronics Assembly V+

V-

water level

Electronics Assembly: Data logger and microcontroller Power amp for bridge Amp for level shifting Batteries

Massachusetts Institute of Technology 12.097

Resistance R = Volts loss per Ampere driven through the device R is not a property of bulk material! Conductance = 1 / Resistance V+ R (Ohms, ) Conductivity of seawater: K ~ 4 S/m, where 1 S = 1 Siemen = 1 Ampere per Volt: One Volt across opposing plates of area 1m2 drives one Ampere 1 S/m means one Volt drives one Ampere, when the distance between electrodes is one meter Conductivity is a property of bulk material! Resistivity = 1 / Conductivity V+ VV-

Equivalent resistance through seawater: R = distance / [ area x K ]

Massachusetts Institute of Technology 12.097

Your Wave Probe


d = wire diameter z = immersion depth D = separation distance

Two wires of immersed surface area dz: Then R = D / [ d z K ] ~ 0.10m / [ x 0.001m x 1m x 4S/m ] = 8
V+ d D
Massachusetts Institute of Technology 12.097

V-

Voltage Divider
TT8 digital i/o OPA551PA amp V1

Rb (fixed)

TT8 analog in

LM324N amp

V2 = V1 Rp / (Rb+Rp)

Rp (WATER)

Massachusetts Institute of Technology 12.097

Wave Probe Electronics Schematic


protoboard +9V _ TT8 D3 (pin A8) OPA551 + -9V 70k +9V _ TT8 AD0 (pin B18) LM324N + GND
+400mV V1 (+5V)

200

8k

V2 9V GND

Probe HOT

Massachusetts Institute of Technology 12.097

Check the Math!


Output of OPA551 is zero (bridge not energized) or five Volts (energized). The voltage divider splits the fixed 200 with about 10 in the water, so V2~250mV. The TT8 AD0 sees about:
(70kW+8k)/8k*400mV 70k/8k*V2 ~ 3.9V 8.8 V2 ~ 1.7V if V2 = 250mV OK
Massachusetts Institute of Technology 12.097

Guidelines to Building
Run the TT8 with a 12V battery always double check polarity! RED IS POSITIVE Youll run the program sclogger; the output will always be written to output.dat. Use ren output.dat myfile.dat to rename the file. Tie the analog and digital grounds of the TT8 to the protoboard. Tie the middle of the two 9V cells to ground; the batteries supply +9V and -9V. Start by building up the OPA551; confirm that V1 is zero when input is zero, and V1 is 5V when input is 5V. When the circuit is complete, use a resistor of around 10 in place of the probe to check the LM324N output. It should be about +1.5V to +2V. When you can log the test circuit output using sclogger, youre ready to go in the water! When you calibrate, the curve should have the form V = k1 + k2 / z TT8 can read 0 to +4095mV, in units of one milliVolt

Massachusetts Institute of Technology 12.097

Hooking up the amps


OAP551 High Voltage High Current LM324N Low-Power Quad

OUTPUT A N/C -IN +IN -9V 1 2 3 4 8 7 6 5 N/C +9V OUTPUT N/C B -IN A +IN A +9V

1 2 3 GND C D

8-DIP (dual in-line pin) 14-DIP


Massachusetts Institute of Technology 12.097

You might also like