Selection Guide to Clamp-On Current Probes
Contents
1. Technical Assistance 800 343 1391 AEMC offers the widest selection of current probes available to measure AC or DC current Several AEMC probes are patented for their unique circuitry and design and the majority are UL approved AC Clamp On Current Probes Theory of Operation An AC clamp on current probe may be viewed as a variance of a simple current transformer A transformer Figure 1 is essentially two coils wound on a common iron core A current 11 is applied through the coil B1 inducing through the common core a current 2 in the coil B2 The number of turns of each coil and the current are related by N1 x 11 N2 x 12 where N1 and N2 are the number of turns in each coil From this relationship 12 N1 N2 x 11 or l1 N2 N1 x 11 This same principle is applied to a clamp on current probe Figure 2 The articulated magnetic core holds gt gt gt Conductor cable 5 N1 B2 N2 mA or A range on Lae your instrument Probe jaws Figure 2 Selection Guide to Clamp On Current Probes pdf 07 02 1of5 www aemc com the coil B2 and clamps onto a conductor where the current I1 is flowing B1 is simply the conductor where the user is measuring the current with the number of turns N1 equal to one The current probe clamped around the conductor provides an output proportional to the number of turns in its coil B2 such that 12 probe output N1 N2 x l1 where N1 1 or Probe2. i Hall Air generator gap Conductor Figure 7 The probe outputs are in mV mVpbc when measuring DC and mVac when measuring AC and may be connected to most instruments with a voltage input such as DMMs loggers oscilloscopes hand held scopes recorders etc AEMC also offers different technologies for DC measurements such as in the K100 and K110 designed to measure very low DC currents and using saturated magnetic technology AC DC probes also offer the opportunity to display or measure True RMS in AC or AC DC Power source AC or DC Current Measurement e Connect the probe to the instrument e Select the function and range Clamp the probe around a single conductor Read the conductor s current value Example Figure 8 AC Probe Model MD303 Ratio 1000 1 Output 1mAac Aac DMM Set to mAac range DMM Reading 125mAac Current in Conductor 125mA x 1000 125Aac DC Probe Model MR521 1mVpc Apbc Hall sensor DMM Set to mVpc range DMM Reading 160mVpc Current in Conductor 160ApDc AC Probe Model MR411 Output 1mVac Aac Hall sensor DMM Set to mVac range DMM Reading 120mVac Current in Conductor 120AaAc DC Micro Probe Model K100 Output 1mVmA DMM Set to mVpc range DMM Reading 7 4mVpc Current in Conductor 7 4mApc Load Figure 8 Technical Assistance 800 343 1391 Selection Guide to Clamp On Current Probes pdf 07 02 ww
3. on probe which will measure low values such as the Model 2610 see page 58 Leakage current on grounds also may be measured directly with the Model MN291 Figure 12 Figure 12 Q AEMC 2002 Chauvin Arnoux Inc d b a AEMC Instruments Selection Guide to Clamp On Current Probes pdf 07 02 INSTRUMENTS Technical Assistance 800 343 1391 www aemc com 4of5 Contact Us United States amp Canada Chauvin Arnoux Inc d b a AEMC Instruments 200 Foxborough Blvd Foxborough MA 02035 USA 508 698 2115 Fax 508 698 2118 www aemc com Customer Support for placing an order obtaining price amp delivery customerservice aemc com Sales Department for general sales information sales aemc com Repair and Calibration Service for information on repair amp calibration obtaining a user manual repair aemc com Technical and Product Application Support for technical and application support techinfo aemc com Webmaster for information regarding www aemc com webmaster aemc com South America Australia amp New Zealand Chauvin Arnoux Inc d b a AEMC Instruments 15 Faraday Drive Dover NH 03820 USA 978 526 7667 Fax 978 526 7605 export aemc com All other countries Chauvin Arnoux 190 rue Championnet 75876 Paris Cedex 18 France 33 1 44 85 45 28 Fax 33 1 46 27 73 89 info chauvin arnoux com Q Selection Guide to Clamp On Current Probes pdf 07 02 INSTRUMENTS Technical Ass
4. output 11 N2 Number of turns in the probe coil It is often difficult to measure l1 directly because of currents which are too high to be fed directly into a meter or simply because breaking into the circuit is not possible To provide a manageable output level multiple turns are set into the probe coil bobbin The number of turns in the clamp on coil are generally simple multiples e g 100 500 or 1000 If N2 equals 1000 then the clamp has a ratio of N1 N2 or 1 1000 which is expressed as 1000 1 Another way to express this ratio is to say that the probe output is 1mA A the probe output is 1mA 12 for 1A or 1A 1000A flowing in the jaw window There are numerous other ratios possible 500 5 2000 2 3000 1 3000 5 etc for different applications The most common application is the use of a current probe with a digital multimeter Take as an example a current probe with a ratio of 1000 1 Model SR604 with an output of 1mA A This ratio means that any current flowing through the probe jaws will result in a current flowing at the output that is 1000 times smaller Probe Output Conductor 1000 times less or 1mA A 1000A 750A 750mA 250A 250mA 10A 10mA 1000mA 1A The probe output is connected to a DMM set on the AC current range to handle the probe output Then to determine the current in the conductor multiply the reading of the DMM by the ratio e g 150mA read on the 200mA DMM range repr
5. Selection Guide to Clamp On Current Probes Selecting The Correct Clamp On Current Probe Answering the following questions will help you to select the appropriate probe for your applications 1 Determine if you are measuring AC or DC DC current probes are categorized as AC DC because they measure both 2 What is the the maximum current you will measure and what is the minimum current you will measure Check that the accuracy at low levels is appropriate or select a low current measurement probe Most probes perform with greater accuracy at the upper end of their range Several probes are designed to measure very low DC or AC 3 What size conductor will you clamp onto This parameter determines the probe jaw size needed 4 What type of probe output do you need or can you work with mA mV AC DC etc Check the maximum receiver imped ance to ensure that the probe will perform to specifications Other factors you may want to consider What is the working voltage of the conductor to be measured AEMC probes must not be used above 600V see specifications What type of output termination do you need lead with BNC lead with 4mm safety banana plugs or jacks to accept 4mm leads Will the probe be used for harmonics or power measurements Look at the frequency specifications and phase shift specifications Lastly if you cannot find information you need or would like assistance call our application eng
6. esents 150mA x 1000 150A in the conductor measured GJ AEMC INSTRUMENTS i AC e Figure 3 J AC Figure 4 j DC Figure 5 Current probes may be used with other instruments with current ranges provided that these instruments have the required input impedance see Figure 3 Current probes may also have AC or DC voltage outputs to accommodate current measurements with instru ments loggers scopes etc with voltage ranges only Figures 4 and 5 This is simply done by conditioning the current probe output inside the probe to provide voltage e g Model MN251 In these cases the probe mV output is proportional to the measured current e g 1mVac Aac Technical Assistance 800 343 1391 AC DC Clamp On Current Probes Theory of Operation Hall effect Differing from traditional AC trans formers AC DC current sensing is often achieved by measuring the strength of a magnetic field created by a current carrying conductor in a semiconductor chip using the Hall effect principle When a thin semiconductor Figure 6 is placed at right angles to a magnetic field B and a current Id is applied to it a voltage Vh is developed across the semiconductor This Selection Guide to Clamp On Current Probes pdf 07 02 www aemc com 2of5 voltage is known as the Hall voltage named after the US scientist Edwin Hall who first reported the phenomenon When the Hall device drive current Id is held c
7. ineers at 800 343 1391 or fax us at 508 698 2118 or email techsupport aemc com GJAEMC INSTRUMENTS Figure 1 Introduction Clamp on current probes are designed to extend the current measuring capabilities of DMMs power instru ments oscilloscopes hand held scopes recorders or loggers and other diverse instruments The probe is clamped around the current carrying conductor to perform non contact current measurements without interrupting the circuit under test The probe outputs a current or voltage signal directly proportional to the measured current thereby providing current measuring and displaying capabilities to instruments with low current or voltage inputs When making a measurement the current carrying conductor is not broken and remains electrically isolated from the meter input terminals As a result the meter s low input terminal may be either floated or grounded It is not necessary to interrupt the power supply when using a clamp on current probe for taking measurements so costly down time can be eliminated True RMS measurements within the probe frequency response are possible by using most AEMC current 7 probes with a True RMS multimeter In most cases RMS measure ments are not limited by the probes but by the instrument to which they are connected Best results are provided by probes offering inherent high accuracy good frequency response and minimal phase shift
8. istance 800 343 1391 www aemc com 5of5
9. onstant the magnetic field B is directly proportional to the current in a conductor Thus the Hall output voltage Vh is representative of that current Such an arrangement has two important benefits for universal current measurement First since the Hall voltage is not dependent on a reversing magnetic field but only on its strength the device can be used for DC measure ment Second when the magnetic field strength varies due to varying current flow in the conductor response to change is instantaneous Thus complex AC wave forms may be detected and measured with high accuracy and low phase shift The basic construction of a probe jaw assembly is shown in Figure 7 Note one or two Hall generators are used depending on the type of current probe The many AEMC AC DC Current Probes were developed based on the above principle together with patented electronic circuitry incorporating signal conditioning for linear output and a temperature compensation network These have a wide dynamic range and frequency response with highly accurate linear output for application in all areas of current measurement up to 1500A Direct currents can be measured without the need of expensive power consuming shunts and alternating currents up to several kHz can be measured with fidelity to respond to the requirements of complex signals and RMS measurements Iq Vh B Figure 6 Gy AEMC INSTRUMENTS Iron core aL
10. w aemc com 3of5 Low Current Process Loop Process Loops Leakage and l Differential Measurements DC Numerous probes are offered for low current measurements For example the Models K100 and K110 have a 50mAbc sensitivity and the Model K110 may be used on 4 to 20mA process loops The selection guide has a special section on low current probes Figure 9 Examples Figure 9 4 to 20mA loop Probe Model K110 Output 10mV mA DMM Set to mVpbc range DMM reading 135mVpc Loop Current 13 5mApc 135 10 When the current to be measured Figure 10 is too low for the probe or better accuracy is required it is possible to insert the conductor multiple times through the probe jaws Figure 10 The value of the current is the ratio of the reading to the number of turns Probe Model SR604 Ratio 1000 1 DMM Set to mAac range Turns in Probe Jaw 10 DMM Reading 60mAac Current in Conductor 60mA x 1000 10 6000mA 6A When the probe is clamped around two conductors with different polarities the resulting reading will be the difference between the two currents If the currents are the same the reading will be zero Figure 11 When a reading other than zero is obtained the reading is the amount of leakage current on the load To measure low currents or leakage Power source A Figure 11 you need a clamp
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