Guide to High Resistance & Microcurrent Testing



Careful reading of the instructions and this guide will help you to perform correct and reliable high resistance and micro current tests. 

Note: Hopetech's HT3544 high precision resistance tester was used for the measurements.


In the voltage addition method for current measurement, the voltage output is 1mV ~ 1000V DC and the internal resistance of the source is 100kΩ.
The resistance measurement range up to 10Ω ~ 1015Ω and the current measurement range 2mA ~ 1pA, can effectively have small resolution up to 10fA.
Measurement functions also include a range of surface insulation resistance tests, surface resistance measurements of insulating materials and semiconductors, and volume resistance measurements as well as volume resistance measurements.


Range Resolution Acuraccy±(%+ Resolution) Temperature coefficient​(ppm/℃)
2 mA  0.1 µA 0.1+5 25
200 µA 10 nA 0.1+5 25
20 µA 1 nA 0.1+5 25
2 µA 0.1 nA 0.1+10 50
200 nA 10 pA 0.1+10 50
20 nA 1 pA 0.3+20 200
1 nA 0.01 pA 5+20 200


Range Resolution Accuracy±(%+ Auflösung) Temperaturkoeffizient(ppm/℃) Prüfspannung
10 kΩ  1 Ω 0.1+5 25 50 V
100 kΩ 10 Ω 0.1+5 25 50 V
1 MΩ 100 Ω 0.1+5 25 50 V
10 MΩ 1 kΩ 0.1+5 50 50 V
0.1 GΩ 10 kΩ 0.1+5 50 50 V
1 GΩ 100 kΩ 0.1+10 50 500 V
10 GΩ 1 MΩ 0.35+20 50 500 V
100 GΩ 10 MΩ 0.35+20 200 500 V
1 TΩ 10 GΩ 2+100 200 1000 V
10 TΩ 100 GΩ 5+1000 200 1000 V
100 TΩ 1 TΩ 10+1000 500 1000 V
1000 TΩ 10 TΩ 20+1000 500 1000 V



If accurate and reliable test results are to be achieved, it is not only the high accuracy of the test instrument itself and advanced test principles that are important, but also the right test methods as well as a suitable test environment. The essence of high resistance testing is to test microcurrents that are very sensitive to environmental, dielectric and material factors. 






1.) The preparation for high-impedance measurements 

Before carrying out high resistance measurements, the following should be noted.



a.) Selection of the environment 

When performing high resistance tests, it is recommended that the user perform the test in dry air to obtain an accurate measurement of the resistance of the item under test. Although the front-end amplifier of the CHT3530 is housed in a waterproof metal enclosure, moist air can contaminate the test probe and the test object and affect the accuracy of the test. 
The test environment must avoid mechanical vibration, which can cause friction between the inner core of the test lead and the frequency shield, resulting in static friction interference. 

b.) Preparation of the fixtures 

Before testing, please prepare the test fixture. If you need to test high resistance, please prepare the electrostatic box. Contaminated fixtures may cause a drop in insulation resistance due to electrochemical effects, resulting in test errors or failure. It is recommended to clean contaminated fixtures with a small amount of a volatile organic solvent (e.g. methanol). 

c.) Electrostatic shielding 

Electrostatic coupling and interference can occur when a charged object is near the input of the circuit under test. At low impedance, the effect of interference is insignificant because the charge dissipates quickly. However, with high-impedance materials, the charge cannot be dissipated quickly, which can lead to unstable measurement results. Since erroneous readings can be caused by electrostatic DC or AC fields, electrostatic shielding helps to minimise the effects of such fields. If available, we recommend that the user perform the test in an electrostatic chamber. If this is not possible, it is recommended to place a metal plate under the object to be tested and connect this to the frequency shielding, which also provides good protection against static electricity. 

d.) Connect the mains cable and the test lead correctly

Make sure that the mains cable of the unit has a good earth connection. Poor earthing of the unit and strong common mode interference will affect the accuracy and stability of the test. After switching on, the voltage output is switched off. For your safety, do not open the charging button until the test leads are connected. 

Connect the correct number of test leads according to the instructions. If you are using an electrostatic box, please connect the wiring correctly to the electrostatic box. 



2.) Test steps  


a.) Switching on and warming up 

In order to achieve the nominal accuracy and stability of the device, the device must be warmed up for 15 minutes before starting the measurement.

b.) Zero calibration of the system 

If the front-end amplifier is not corrected for "zeroing", the resulting bias voltage will overpower the input signal and produce an error due to the presence of detuned voltage and current. The bias is usually expressed as a function of time or temperature. The zero offset over a given time and temperature range should be within the specified limits. Distortion caused by temperature jumps may exceed the given specification before reaching stability. A typical rate of change of room temperature (1°C/15 minutes) will not normally cause such overshoots. System zeroing is normally only required when the unit is first switched on or after an extended period of testing due to a large change in the environment.  
To perform: Enter the system calibration icon without entering the password to access the menu, and hold the test port in a well-opened circuit for 5 seconds (5 seconds is the set-up time described in the following section), press OK to perform the system zeroing, and wait until the zeroing reaches 100% before exiting the menu. 

c.) Clearing the background current (panel zeroing). 

Background current is the drift of the base due to changes in bias current caused by factors such as changes in leakage of protective devices, test leads, etc., or changes in the test environment or changes in the electric field during the test. The input bias current is superimposed on the current under test so that the meter measures the sum of the two currents: IM = IS + IOFFSET. 
of some of the factors. When removing the background current, try to keep all live objects (including people) and conductors away from the sensitive areas of the test circuit and avoid movement and vibration near the test area. 


has a large base when the measuring end is open, you must set it to zero. This can be done by pressing the "Clear" button on the test screen. Do not touch or shake the test leads when doing a clear, but keep the test leads well open. It is a good idea to leave the test leads hanging until the set-up time has elapsed and the soil number is stable. Note: There is a difference between system zeroing and panel zeroing.


d.) The system zeroing

System zeroing is achieved by adjusting the internal bias of the unit, which improves the linearity of the unit and reduces misalignment. Zeroing the indicator is a simple subtraction operation to subtract the base of the indicator. Connecting the UUT The UUT is placed in an electrostatically shielded environment (to avoid interference from static fields), and the UUT and shield are placed in a highly insulated condition that prevents the measured current from being bypassed.  

Try to avoid excessive twisting of the sampling line, as the cover line produces a piezoelectric effect when twisted and static friction when stretched slowly, which can cause test errors or erratic readings.

Voltage output 
From the measurement screen, press the tension setting button and enter the desired test tension. Make sure the test terminal is open and press the "Charge/Discharge" button to output the voltage, which is then output at the high voltage output. 

e.) Test start 

It is normal for the test to take some time to stabilise. This time is related to the resistance and stray capacitance of the test object and the material properties of the test object and is usually referred to as the set-up time (see next section for details). During the test, keep all live objects (including people) and conductors as far away as possible from the sensitive areas of the test circuit and avoid movement and vibration near the test area. No measurements can be taken until the set-up time has elapsed. 


f.) End of measurement

End of measurement Press the "charge/discharge" button to switch off the voltage output and remove the DUT. 


g.) Repeated tests

To ensure the reliability and authenticity of the data, the user can repeat the process of steps (c) ~ (f).






3.) The construction duration 

The build-up time of the circuit is particularly important when measuring high resistances. The build-up time of the measurement is influenced by the parallel capacitance
which is generated by the connecting cable, the test fixture and the test object. The parallel capacitance (C) must be charged to the test voltage by the test current (I). The time required to charge the capacitor is determined by the RC time constant (doubling time constant) and results in the well-known exponential curve. This requires a waiting time of 4 to 5 times the time constant before an accurate reading is obtained. When measuring very high resistance values, the build-up time can be several minutes, depending on the value of the shunt capacitance in the test system. For example, if C is 10pF, the time constant for measuring a resistance of 1TΩ is 10 seconds. Therefore, a build-up time of 50 seconds is required to stabilise the measured value at 1% of the final value. To minimise the set-up time when measuring high-impedance resistors, the connecting cables are kept as short as possible so that the parallel capacitance in the system is actually as small as possible. In addition, set-up time can be significantly reduced by using protection techniques. Finally, resistance measurements using the voltage and current measurement method are generally faster because of the reduced set-up time.

Note: To obtain more accurate and stable measurements, it is recommended to set the instrument's test speed to "slow", the average number of tests to "20", and when testing new products, to wait for a start-up time of about 30-50 seconds before viewing the measurement data.




4.) Test the connection

The cable between the input end of the instrument and the device under test must also be shielded. The capacitive coupling between the electrostatic noise source and the signal conductor or cable can be greatly reduced by enclosing the signal conductor with a metal shield connected to the ground end. With this shielding, the noise currents generated by the electrostatic voltage source and the coupling capacitors flow through the shielding to earth and no longer through the signal line.




In general, observing the following guidelines can minimise the current generated by electrostatic coupling:

In general, the following guidelines can be followed to minimise the currents generated by electrostatic coupling.  
* Keep all live objects (including people) and conductors away from the sensitive areas of the test circuit.  
* Avoid movement and vibration near the test area.  
* If the measured current is less than 1nA, shield the device under test by surrounding it with a metal cap and connecting this cap to the common end of the test circuit. If an insulated electrode test box is available, the part under test can be placed in the electrode box for testing. 



HT3544-DC-reistance-meterWiderstandtester Serie HT3544

The HT3544 Precision DC Resistance Tester is one of the most accurate DC resistance testers in the industry. The HT3544 DC resistance tester has a 3.5 inch display and has a measuring range from 3mΩ to 3 MΩ. With a minimum resolution of 0.1 μΩ and a measurement accuracy of 0.02%, the resistance tester is well suited for inverter motor inspection and other applications requiring high-resolution resistance measurement. Equipped with RS232/RS485/LAN interfaces and EXT I/O port, the devices of the HT3544 resistance tester series are suitable for performing automatic tests in test or production lines.