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AC current sensor compatibility CR800 + AM 16/32

Benjamin.vial Dec 28, 2020 11:18 AM


I'm looking for a AC current sensor just like the CS11, but significally smaller, to monitor 2.5mm² wires.

Campbell sell only the CS11 from a CR8459 current transformer, but I see on the constructor website (crmagnetics) there is a CR8401 model, smaller. So multiple questions :

1 - Is this compatible on a CR800 ? I'm not sure what specifications are to be worried of.

2 - How many sensor of this type can be plugged on a CR800 (if we consider there is no other sensor)?

3 - Can we increase the number of this type of sensor with a AM 16/32 plugged on the CR800 ?



JDavis Dec 28, 2020 08:14 PM

The input range on a CR800 is -5VDC to +5VDC. As long as the sensor output is within that range, you can read it on a CR800. If you are looking at raw current transducers, you have to add a resistor to change the output from a tiny current to a voltage. Looking in the CS11 manual, you will see a diagram showing how Campbell Scientific adds a resistor.

Each transducer needs 1 SE channel. There are six such channels on a CR800. 

A multiplexer could be used. Be aware that it takes time to do channel switching, so will limit how fast you can sample the full set of sensors.

Benjamin.vial Dec 30, 2020 01:35 PM


thanks for your answer.

About the +-5Vdc input voltage range I've looking on the specifications (from CRMagnetics) of the CR8459 and can't tell if that can be used. It works of course, as CSI send it on their website, but can't see on the doc where to understand it.

As I cant see where to know what is the minimum current seen (but I see the max). On CRMagnetic's doc it seem that the CS11 is a "revenue grade current transducer", because the CS11 can measure 200A maximum. But the 8401 don't exists on the grade... So I think to buy the CR8401 for general purpose to see <10A AC current, and some CR8420 to see <50A for power supply monitoring applications.

And about the multiplexer I think make a scan period about 10 minutes so no worry about the response delay.

Other question, with CR8401 instead of the CR8459, can I use the ACPower function in CRBasic editor ? I've looking for the resistance information in the CS11 documentation but can find it too ...

Sorry, it seem I don't really understand how to choose the sensor in this case !

(here is the link to the crmagnetics doc for the CR84XX series : https://www.crmagnetics.com/Assets/ProductPDFs/CR8400%20Series%20Specification%20Page.pdf)

JDavis Dec 30, 2020 05:22 PM

I usually recommend selecting sensors from Magnelab. It is clear what output signal the sensor has when ordering.


0.333VAC output signals work well with the ACPower instruction.

Benjamin.vial Nov 23, 2021 02:37 PM


I come back on this topic. I'm using a CR800 to read a magnet CR8448-2500-N, very near of the CR8459-2000-N sell by CSI. I have result of measure but, I guess there is some value to change in the program. Here it is :


'CR1000 program to measure rms current
PipeLineMode 'must be pipeline mode

Const num_samples = 100 '100 Samples @ 1000 micro sec = 0.1 second (5 @ 50Hz or 6 @ 60 Hz).
Public Amps 'the line current
Public Amp_mult
Dim i_sig (num_samples) 'to hold the burst measurements, each 100 samples long
PreserveVariables 'to store values between power cycles

DataTable (AmpTable,True,-1)
  DataInterval (0,1,Min,10)
  Maximum (1,Amps,IEEE4,False,False)
  Average (1,Amps,FP2,False)
  Amp_mult = 0.2 '0.2 multiplier for the CS10-L
  Scan (250, mSec, 10, 0)
    VoltSe (i_sig (1), num_samples, mV2500,-1, True, 1000, 0, 1.0, 0)
    StdDevSpa (Amps, num_samples, i_sig (1))
    Amps = Amps * Amp_mult 'put in amps
    CallTable (AmpTable)


I never use this kind of program structure, I'm not totally sur of what is doing... I found it on CS10 manual.

For example, there is a very fast scan frequence (because of the 50Hz alternating current I guess), how can I add some simple SE measure or a differential measure with out use this high frequency ?

Another point, the "Amp_mult" multiplier is 0.2 for the C10-L (retired product but same magnet as CS11), but how can I find it for my magnet this is the same multiplier to apply ? I read the manual and see the A-5 page speaking about it, there is a R of 10 ohm, and according to the datasheet it should be 74 ohm, so what this value of 10 ?

Here is a graphic of what I measure whit several hours of reading a battery charger, swithed on and off sometimes.



JDavis Nov 23, 2021 04:07 PM

It will simplify your program greatly if you use the ACPower instruction. The example from the CS10 manual predates the ACPower instruction.Without also having a voltage measurement, some outputs of ACPower() will not be valid but the current measurement will be correct.

Benjamin.vial Nov 24, 2021 08:51 AM


thanks for your answer.

Ok I'm trying the ACpower instruction. I understand that this instruction is for a AC sensor that can measure both voltage and current. I have values but not sure if it's correct

I making further investigations to understand what I'm reading now :-)

I will come back later to say if everything is ok.


Benjamin.vial Nov 25, 2021 08:15 AM


well, I have a NAN measure when alternating current is on and something about 0,34 mV when it's off.

I tried to use the ACPower instruction but the default Vmx RMS is 120, and on the CR8448 datasheet it's 6,6 Vmax RMS ; I tried to put 10 : same results.

Here is my program :

Dim CS11Array(7)
Public BattV
Public PTemp_C
Public Amperage
Public SEVolt

Units BattV=Volts
Units PTemp_C=Deg C
Units Amperage=A
Units SEVolt=V

'Define Data Tables


'Main Program
	'Main Scan
		'Default CR800 Datalogger Battery Voltage measurement 'BattV'
		'Default CR800 Datalogger Wiring Panel Temperature measurement 'PTemp_C'
		'CS11 Current Transformer measurement '5'
		'Generic Single-Ended Voltage measurements 'SEVolt'
		'Call Data Tables and Store Data
		CallTable current
		CallTable soh


There are two instructions that I don't understand :

Dim CS11Array(7)

There are 7 values to put in variable CS11Array, but why 7 because there is another one,


Here there are 4 values.

I'm running out of idea ...

EDIT : I just found this on the CS1 documentation :"When using the
ACPower() CRBasic instruction, another sensor, a potential transformer, is
required in addition to the CS11 sensor to obtain all of these measurements and

I miss that on the first read. What kind of potential transformer I need ? Can I have current measure without using ACPower instruction ?

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