# Measuring Voltage and Curent Simultaneously with Probe?

I have very little experience with electricity, but I am doing a project in which I need to measure power output of solar cells.

I am currently using this: http://www.pasco.com/prodCatalog/PS/PS-2115_pasport-voltage-current-sensor/index.cfm with GLX software to measure voltage/current over time/temperature. When I measure either voltage or current, the values are correct - as checked by a multimeter.

However, when I try to measure both simultaneously - which I must do - the values seem to equalize at around 0.5 for each - incorrect for both values.

I know I can just use a multimeter and record that way, but I need to be able to do this hands free and simultaneously.

Is there a circuit or something I can use or setup that will help me measure both accurately and simultaneously?

Kinda embarrassed to post this, but i guess I'll never learn otherwise.

simulate this circuit – Schematic created using CircuitLab

The battery is supposed to represent the PV cell. The voltmeter/ammeter next to each other are supposed to represent the probe with its dual function. Can you suggest any other way to set it up and/or is there major problems with what I am doing (probably numerous).

• 1) It's hard to answer your question without knowing how you've hook up your 2-in-1 measurement device. Please post a schematic and/or a photo. Welcome to EE.SE, by the way. Commented Dec 2, 2013 at 1:55
• 2) Does your measurement device bring down the voltage in the line? Does it produce the [allegedly] incorrect measurements without altering the measured parameters? How do you know that 0.5 [units?] is incorrect? Commented Dec 2, 2013 at 1:56
• Are you connecting the leads in accordance with the manual? The voltage leads go across the solar cells while the current leads have to be in series with the solar cells. What are you using as a load for your solar cells? As mentioned above, a schematic of what you are doing would make it a lot easier to diagnose your problem. Commented Dec 2, 2013 at 2:09
• I don't think this instrument will work on PV panel as the current source can be high impedance. I suggest two meters or a switch.
– user33465
Commented Dec 2, 2013 at 2:21
• Using two meters might be great, but I am measuring the change in these values over a long period of time. Thanks for the really quick responses. Commented Dec 2, 2013 at 3:15