They can be totally isolated from another high voltage electrical system which eliminates many safety concerns. In other words when the wire that is carrying current passes through the donut shaped hall effect current clamp shown below in the picture, it is not conducting at all with anything on the sensor at all. The sensor is just measuring the magnetic field from the wire. This is a nice advantage over current monitoring shunt precision resistors which are less safe because they require you to put in certain safeguards to protect your data acquisition system.
If you are not getting the resolution you want, you can loop the wire through the current clamp as many times as you want to double, triple, or quadruple the sensitivity or resolution of your sensor. For example, if your current signal is only .03 Amps, you could loop the wire through the sensor 10 times and the signal would by 10X stronger and would appear as 0.3 Amps.
Unlike the current shunt sense resistor which can have thermal temperature heat dissipation issues, the hall effect current sensor does not get hot. Even when measuring 50 Amps!

Below is an example of how you can hook up a hall effect current sensor to a PIC micro controller which sends the DC power data out an RS232 Serial Com Port to your computer. You can use HyperTerminal or WattsVIEW to see the data.

Click here here if you want to buy an off the shelf current sensor?

HOW IT WORKS Hall Effect Current sensors mounted on a circuit board to measure pedal power current

Below you will see a data table and graph showing the relationship between current and sensor output voltage. In this case, the sensors were mounted on a circuit board made by youngbloodtech.com . The hall effect sensor I chose to use is the CSLA2CD found at many distributors like Digikey for $18.00.

The current sensor was supplied with 8 Volts DC from an on board regulator. You can see that when there is no current flowing through the large red wire, the sensor simply divides its supply voltage in half (8V divided by 2 = 4.0 Volts output).

However, for every amp that flows through the wire, the voltage output from the sensor increased about 0.033 Volts.

Amps	Response From Sensor
0	4.000
1	4.034
2	4.063
3	4.098
4	4.127
5	4.161
6	4.200
7	4.229
8	4.259
9	4.293
10	4.327

power Chart Graph Hall Effect Current Sensor Output 33mV per amp current bike generator

You can buy a hall effect transducer clamp off the shelf to measure AC and DC current for $50 to $400. Or you can build your own. Digikey sells many types of these sensors. I have used the ones below made by Honeywell before.

Measureing DC or AC current with a Hall effect transducer DIgkey hall effect transducer

digikey part numbers for Honeywell current transducer

Digikey Honey well current Hall effect sensor specifications and pricing

I like the Open Loop Linear CSLA2CD model because I like to read the voltage output instead of current output, and this sensor also can detect AC or DC current. Here more details about this sensor:

Data sheet:

THIS FROM THE MANUFACTURER - HONEYWELL

Features

Linear output
AC or DC current sensing
Through-hole design
Fast response time
Output voltage isolation from input
Minimum energy dissipation
Maximum current limited only by conductor size
Adjustable performance and built-in temperature compensation assures reliable operation
Accurate, low cost sensing
Operating temperature range -25 �C to 85 �C
Housing: PBT polyester

Typical Applications

Variable speed drives
Overcurrent protection
Ground fault detectors
Current feedback control systems
Robotics
UPS and telecommunication power supplies
Welding power supplies
Automotive - Battery management systems
Wattmeters

Description

Honeywell CS series linear current sensors incorporate our 91SS12-2 and SS94A1 linear output Hall effect transducter (LOHET�). The sensing element is assembled in a printed circuit board mountable housing. This housing is available in four configurations. Normal mounting is with 0.375 inch long 4-40 screw and square nut (not provided) inserted in the housing or a 6-20 self-tapping screw. The combination of the sensor, flux collector, and housing comprises the holder assembly. These sensors are ratiometric.

To use these Hall effect transducers you need to hook up an excitation voltage shown in column 2 of the table above. This creates a magnetic field inside the loop AKA "Clamp". I used the $19 480-1994-ND sensor to build a power sequencing test rack for computers and servers. I used LabVIEW to control HP power supplies which provided 3V, 5V, and 12V to the computers in an environmental chamber. LabVIEW would read these Hall Effect sensors for each of the voltages and show on a graph the exact current that the computers and servers were consuming.

With no current going through the loop they put out about half of the voltage you are supplying. So if you have 10V DC supplied to this sensor, you will see about 5VDC coming out of it. You can wire this to a data acquisition box like the LabJACk and use a software program like LabVIEW to get waveforms like an Oscilloscope gives you. Here is a software program I wrote using the LabJACK data acquisition box. The picture shows 5th grade students loved watching the power racing against each other and seeing how much power each bike generator created:

If you want to use an off the shelf solution you can consider something like these devices below. BEWARE - many of these clamps measure only AC current. So check the specifications to make sure it says AC/DC like these ones below. You will find the AC/DC current clamps are more expensive than just AC current clamps.

This is a inexpensive hall effect transducer current monitoring clamp and voltage meter. The Loop that you see is called a "Clamp".

To use it, just push down on the lever shown on the left and the clamp opens. Then you put it over one of your wires coming from the generator. Power = voltage times amps. So when you get measure the amps going through the wire, then multiply it times how much voltage is coming out of your generator. That gives you watts.

More Info Here:

Extech EX710 800 Ampere Clamp Meter

This fluke current clamp can be used to do continuous current monitoring either with your hand held DMM digital multi-meter or you can also use a USB data acquisition device like the LabJACK U12 (shown below) which will allow computer software act a as power monitor software oscilloscope. When you download the free software for this LabJACK, it comes with free voltage monitoring applications called "LJstream1" and "LJsimplelog". This will plot and data log your power generated. LJsimplelog will log data from 8 Analog input channels at a rate of 25 samples per second. This LJsimplelog is usually fine for most DC power applications, but is too low of a sample rate for AC power which usually runs at 60 hertz or more. If you want a faster data logging program, i can write one for you using LabVIEW. Send me an email at support@scienceshareware.com

FYI: For current voltage and power data logging to tab delimited text files or chart recorder, you will want to do continuous analog voltage signal to hook up to a data logger so you can monitor current or power over a few hours or even days time. The graph shown in the image below and on the projector white -screen in a class room activity is giving what they call "Real Time" voltage / Current / Watts plot data. Power = Amps X Volts so you have to monitor current and voltage and then multiply them times each other to get Watts.

This would allow you to calculate KW Hours to see how much total power has been used or created.

IF you want this LabVIEW software send an email to support@scienceshareware.com

Fluke I410 AC/DC Current Clamp for DMMs - 400 Amp

U12