My daughter wants to do a science fair experiment that involves reading the electrical signals in plants, but the cost of a multi voltmeter with data logging is very high. Can anyone suggest a setup for less than $100? Maybe she doesn't need as complicated a set up if she tests one plant at a time? But I believe that the sampling rate has to be at least 3000 s/sec.
Here's a setup for a similar experiment: A PXI-4071 digital multimeter (National Instruments, Austin, TX, USA) connected to .2-mm-thick non-polarizable reversible Ag/AgCl electrodes was used to record the digital data. The PXI-4071 high-resolution digital multimeter delivers fast voltage measurements from 10 nV to 1000 V, current measurements from 1 pA to 3 A and resistance measurements from 10 µΩ to 5 GΩ. A
Update: One of the researchers in this field answered my daughter's email and said that she could use a KEITHLEY DMM. Would that still require an amplifier? The only affordable ones on ebay (models 169, 177, 179) only have a digital read-out, no PC interface. I'm guessing she needs some sort of output recording device, like an oscilloscope? What about a Radio Shack MM with PC interface and op-amp (on a breadboard?)?
UPDATE: She ended up using a RS digital multimeter w/PC interface. The software was easy to use and the data could be saved to text files on the computer. For each test, the DMM took a reading every second for 100 seconds (there are other options too). The MM was set to record mA. I chlorided 30 gauge silver wires with bleach for the electrodes. Those worked OK, but maybe could have been thicker and not bent as much. The DMM did measure a strong reaction from the plant when it was stressed with high heat (brass wire attached to brass woodburning pen) applied for 5 sec. The baseline voltage seemed to vary alot from day to day (over 20 days), but I'm thinking that's because the electrode was touching a different leaf or part of a leaf on each day. Next time, it should be in the same place for each plant over all the days. Thanks for everyone's advice!