Measure Amps With a Sensor
Measure Amps With a Resistor
Measure Amps With A Meter
Measure AC and DC Current Amps using a Hall Effect Current Sensor Transducer
There are three key advantages to using hall effect current sensors transducers:
They can be totally isolated from another high voltage electrical system which eliminate risk to delicate monitoring equipment and also minimizes safety concerns. In other words this sensor only detects the magnetic field around the wire, there is no electrical contact between the sensor and the wire. This is a nice advantage over using a current monitoring shunt precision resistor.
If your signal is too weak or you are not getting the resolution you want, you can simply 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!
Example Wiring Diagram For the CLSA2CD Sensor Sold HERE on Amazon.com.
The diagram above shows a 12 Volt DC wall adapter supplying voltage to a 8 Volt regulator. The 7808 Volt regulator puts out a very stable DC voltage. This is very important because the sensor outoput is only ~0.032 Volts per Amp that it measures, so if the voltage you are supplying the CLSA2CD is noisy, your data will get lost in the noise. The ground is shared through out the circuit. You could mount these components on a small piece of proto board like the one shown below. Or if you want to get one already assembled take a look at the one sold at http://measure-current.com
HOW IT WORKS
Below you will see a graph showing the relationship between current and sensor output voltage. In this case, the sensors were mounted on a circuit board.
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.
The formula you could use to convert from Volts to Amps is as follows:
Measured Current = (Vsensor - 4.0) / 0.033
So for example if your sensor puts out 5 Volts, then your measured current would be something like:
(5V - 4V)/ 0.033 = 30 Amps
For Purchase Information Go To http://measure-current.comEXAMPLE DATA FROM SENSOR - SOLAR PANEL / BATTERY CHARGING APPLICATION
Below you can see real data from just one sensor for a solar panel / battery charging application. The green trend line represents data from the sensor. The red trend line has been converted to Amps using the following linear equation. Amps = ( Vsensor - 4.0) / ~33mV
As the sun comes up, current slowly flows into the batteries rising from 4 Volts DC to 4.5V DC. This corresponds to a current range of Zero amps up to 16 Amps shown in red on the right side of the graph.
When someone in the home turns on an electric appliance then the current goes negative down to 2.6 Volts DC because it changes direction as it flows from the batteries into the House AC inverter which could be powering something like a refrigerator or washing machine. A value of 2.6 Volts DC output converts to a current value of ~ -45 Amps. Assuming these batteries are setup in a 24 Volt configuration, then you could use this current measurement to approximate how much power your batteries are putting out. In this case it would be about 1,080 Watt power output to the inverter.
(24V X 45A = 1080 Watts)
Below is an example of how you can mount a this current transducer on a circuit board. If you want to get order information for this device click HERE.
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.
I like the Open Loop Linear CSLA2CD model because it puts out a linear voltage signal , and this sensor also can detect AC or DC current. You can buy this sensor on Amazon.com
Here more details about this sensor:
THIS FROM THE MANUFACTURER - HONEYWELL
- 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
- Variable speed drives
- Overcurrent protection
- Ground fault detectors
- Current feedback control systems
- UPS and telecommunication power supplies
- Welding power supplies
- Automotive - Battery management systems
Description Honeywell CS series linear current sensors incorporate our 91SS12-2 and SS94A1 linear output Hall effect transducer (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.
This type of current sensor / transducer requires a DC voltage to operate. For the CSLA2CD 72 Amp sensor you need to hook up an excitation voltage anywhere from 5.4 Volts to 13 Volts. I used this 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.
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:
This fluke current clamp can be used to do continuous AC or DC 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 to act as a 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 email@example.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.
Fluke AC/DC Current Clamp
Below are a few configurations showing what you can monitor with the hall effect current transducer.
More questions? Send an email.l.