Main Site Documentation

Current Sensor Information


#1

:o :o :frowning: >:(
I just found out from Seeed Studio tech support that the current sensor is made for high AC currents such as 100A. But they also said that it should work for currents above 100mA. Both GHI and Seeed Studio websites did not povide this information in the catalog pages.
Mine could not accurately detect 500mA. The values are all over the place. And iI have to pay a restocking fee to return the bad sensor. So beware, you may get mine.


#2

100A :o I can’t think of too many Gadgeteer projects that would ever monitor that kind of juice. I don’t have any experience with Seeed, but GHI is very good about “making things right”. A restocking fee is just pouring salt on the wound!


#3

There is no restocking fee if there is an error. Your email said you didn’t like the sensor and you want to send it back and so there is restocking fee :slight_smile:

In this case, we will track this down with seeed and if the info provided on website is not correct then you get full refund as this is is our (actually seeed’s) error.

You are in good hands, do not worry.


#4

;D
I started out with real excitement about Gadgetteer and GHI until recently. But your reply is making me feel better.
I did say that I didn’t like the sensor because it doesn’t seem to be working and no one has been able to help.
Here’s the link to the Seeed forum topic:

http://www.seeedstudio.com/forum/viewtopic.php?f=4&t=2868


#5

A single module should not put you off. I just got mine today and I have say this is too cool for school. Will be interested to see the ma reply.


#6

@ William - this is just right for the fight (to help get STEM education get back on track in the US) :slight_smile:


#7

@ mariok88

The current sensor module for gadgeteer should actually be rated at 30A. There should be a model code (SCT-013-030) printed on the current transformer (CT). Googling this code will give you all the details on the current transformer. The 30A CT’s are usually used for monitoring electrical usage in the home at the circuit breaker panel. The resolution isn’t very good for low amp measurement.

The model SCT-013-000 is rated at 100A, but I would be surprised if you have this one.

Also, the direction of the CT on the line matters. Generally, CT’s have an arrow and the CT needs to be attached to the line in the direction of the load. Try flipping the CT on the line and see if your readings improve.

You can also try testing with a blow dryer plugged into your circuit as it will draw a lot of current. This will at least verify the CT and module are working correctly.

You can buy 5A CT’s, but you’ll need to create your own 3.55mm connector for the Gadgeteer module. Here’s one place I just found http://www.powermeterstore.com/c1015/solid_core_current_transformers.php but you can find others by googling “ac current transformer 5a”.

Finally, these type of CT’s don’t really go smaller than 5A, but a 5A CT may give you good enough resolution for low amperage measurement depending on what you’re looking for. For finer resolution at low amperage, I think you need a current sensor IC.

Hope this info helps.


#8

Hi, everyone , maybe the seeed gays do not express this module and its driver clearly.

  1. The current sensor module is an current transformer that has a turn ratio of 1800:1 , the current measured can be upto 30A. it also has a build-in sampling resistance of 62Ω, that is, when the input current is 30A, the output voltage would be : 30/180062≈1V. as the spider ADC ref is 3.3v and the ADC is 10bit , so the minimum resolution would be :303.3/1024≈100mA. Attached the datasheet of the module.
  2. Actully , this module is just a transformer, it can not convert AC to DC or measure the AC current directly. If in use of measuring AC, we need to sample the voltage repeatly, to find out the max of the sample voltage, the numbers of the ADC should be enough to guarantee the peak value or value close to the peak was sampled (that is to say, the sample times should be more than a period of the signal). like the code below:
public double GetCurrentReading()    
      {            
           double current = 0;             
           double max = 0;             
           for (int i = 0; i < 200; i++)            
                 {                 
                    current = analogInput.ReadVoltage();                
                      if (max < current)               
                                   {                     
                                           max = current;            
                                   }           
                  }                 
                      return max * 30;             
             }  

we sampled 200 times and finds out the max, and then multiply with the ratio, to get the peak of the AC current. If we need the equivalencevalue, you can divide it with a 1.414…

in this way, I get the current of my air conditioner
10.1513671875
10.0546875
10.0546875
10.1513671875
3. as the spider kit in my hand, if I sample the voltage in my user application, the ADC speed is too low, but if I do the sample in the driver, it is much more faster. So , I think , how about modify the module driver like this: set 2 functions , one is GetDCCurrent() and the other is GetACCurrent(), in the GetDCCurrent(), only one ADC was needed. In the GetACCurrent(), hundreds of ADC was needed to find out the peak value. In this way, the driver would be more easy to use.


#9

I would have expected the module to have a diode/cap to make this DC! We have set this to “out of stock” till GHI does more testing on it and get more info from seeed directly.


#10

Thank you Gus. I had ordered one of these sometime ago in anticipation of an upcoming project, but after seeing this thread I thought I would test it with both the Hydra and the Spider and frankly it appears to be making up data as I tried it on a number of devices and appliances. Needless to say I’m a little disappointed in Seeed as I’m wondering if they did any testing or product QA as it appears a couple of us have non-working current senors, the ball is in their court and I’m waiting to see what they do with it.

I know I can trust GHI Electronics for well designed and quality checked components from a company that actively stands behind their products and customers (and I have proof of that), and I hope that Seeed can step up their game suitably (I just bought another bucket of modules from them, but I’ll be holding off on buying more until I see how this plays out).


#11

This is all just extra background info - not suggesting there’s no need for additional information or investigation here.

I think you might find Seeed have a long history with the current sensor clamps, and I’ve not seen any negative discussion on them. They are after all pretty basic units. The “new” is really how they’re connected to the Gadgeteer world.

They do contain resistor or diode, depending on the sensor type, as you can see on the individual sensor page http://www.seeedstudio.com/depot/noninvasive-ac-current-sensor-30a-max-p-519.html?cPath=144_154. Since this 30A one is a voltage output type, it will contain the bias resistor. The 100A unit is a current output device so it will have an inbuilt diode. Given they’re different, they are probably not interchangeable for use with the gadgeteer module.

You also need to know how to connect these sensors. Explicitly, it needs to be over one of the AC wires for instance in a switchboard - you can’t just put it over your everyday household shielded cable from the toaster, since it has multiple cables for Active Neutral and Earth. These sensors use the magnetic field generated by the current flow in the conductor, and if you tried to measure that over both the Active and Neutral, you essentially get a nulled out value. But measure it just over the Active and you will measure the current that the device is drawing.


#12

GHI is still investigating …


#13

Trying to be as fair as I can, I went bought a short extension cord where I could seperate the 3 lines, such that I could place the sensor around one of power lines as suggested and while I did see an increase in the sensor reading, they are in the order of 23-26 amps which is far to high for what is actually flowing.

Another test I use is what the readings should be if I open the sensor, or close the sensor without a wire in it or a wire with no power condition (ie zero conditions) in all these cases I get readings in the 5.8 - 8.7 range (using a Hyrda).


#14

hi all, a new driver for the current sensor has been released to codeplex, check if works for you… :stuck_out_tongue:


#15

I’m sorry to have to ask, but where on Codeplex?

Thanks


#16

#17

After a quick test this does look better, perhaps a tad high but still in the ballpark.

I’m still a little concerned if we should be using just the PeakValue and perhaps shouldn’t also add some form of averaged value if were are doing a power consumption type app for example (but still the sensor still reports a small current in a zero condition (ie sensor open or no wire in the sensor, or no power wire) so a power consumption device might not be very accurate.


#18

@ Duke, what did you use to test it?


#19

1500 W toaster with a hacked up cable (ie I bought a short 3 line extension cord and then cut the lines apart so I could put the sensor on a single line). So with everything going on the toaster it should have been drawing about 12.5 A, but the sensor was reading higher but that might explain why when the toaster is going turning on the microwave usually results in a trip downstairs :slight_smile:

It was just a quick test that looked a heck of a lot more reasonable then my previous quick test.


#20

by my calcs, 1500w toaster should show ~13.6A if you’re on 110v, 6.25A if you’re on 240v. What is your nominal voltage, and how different was your reading to 13.6A?