Innovative series of insulation resistance meters

Difficulties encountered during high-voltage measurements of insulation resistance and the increasing requirements set for professional instruments motivated Sonel engineers to develop a new family of insulation resistance meters. As a result, the launch of four new-generation products has been announced, with MIC-5010 and MIC-5005 models being currently available for users.

The biggest challenge for Sonel designers was to reconcile two apparently opposite features of the devices: very high resistance to external interference and the capability to work on tested objects with the presence of induced voltage while ensuring maximum safety during all measurements. Most of the meters currently available on the market carry out a simple test before the measurement to check for the presence of voltage on the object. Detecting no voltage above a certain value (usually around 25 V) allows the measurement to be started.

The new family of Sonel insulation resistance meters uses unique algorithms to identify the type of voltage present on the tested object, so that the device can distinguish between mains voltage, when no measurement is made, and voltage generated by electromagnetic field, when the measurement is carried out and the result shown on the display. This allows measurements to be made in the presence of very strong electromagnetic fields, which was previously impossible.

The first models in the new series, MIC-5010 and MIC-5005, are capable of performing the following measurements:

insulation resistance with preset voltages: 100V, 250V, 500V, 1000V, 2500V and 5000V,
insulation resistance with voltage adjustable within the range from 50 to 5000V (every 10 or 25V),
DAR, PI and Ab1, Ab2 coefficients,
step voltage insulation resistance (SV),
Dielectric Discharge calculation (DD),
In addition MIC-5010 measures the continuity of protective connections and equipotential bonding with current ≥200 mA.

The devices are equipped with appropriate accessories for maximum safety when performing measurements with all available voltages - both test leads, probes and “crocodile” clips meet extremely stringent standards (guaranteed voltage stability up to 11kV for test leads and 5.5 kV for crocodiles and probes). The accessories are normally supplied together with a portable case. Even leads up to 20 m long can be used for measurement due to the high resistance to interference of the unit.

Due to their overall dimensions which are necessitated by the kind of power supply needed to ensure a high current efficiency and electrical safety standards, the devices are enclosed in a portable case providing the ability to operate in harsh environmental conditions (IP 67 - with lid closed) and high measuring category CAT IV 600 V (CAT III 1000 V). The 5.6” screen displays the results in a clear way: the main value, bar graph and additional information. Switching between measuring voltages and functions is carried out by means of a knob, while options are selected by pressing assigned buttons. The menu enables the selection of general measuring parameters and functions. The display (in both models) and keys (MIC-5010) are backlit making it easy to work in limited visibility. The presence of voltage at the terminals when measuring is indicated by LEDs. If necessary, the case lid can be easily removed to facilitate measurements in specific circumstances.

An important parameter of the instruments is the maximum measured value of insulation resistance up to 15 TΩ. The maximum test current of 1.2 mA or 3 mA (selectable) guarantees the charging of high capacitance objects in a short time. Each measurement interrupted after timeout or manually, ends by discharging the object by the meter, which is accompanied by the real time display of the voltage drop. Measurement time is user defined up to 99 minutes 59 seconds. MIC-5010 and MIC-5005 stand out from other similar devices in that they also measure the DAR, PI coefficients during insulation resistance measurement (or Ab1, Ab2 - to be chosen by the user; the time of resistance readings for calculating the coefficients may be selected by the user – up to 600 s), so there is no need to run a separate measurement function. After the measurement is completed, all the results (resistances measured at specific times, absorption ratio, tactual voltage during the measurement, leakage current, capacitance of the object) are saved in memory.

Two- or three-wire insulation resistance measurement can be performed to eliminate the impact of surface leakage currents. In addition the meter is equipped with the function of (hardware and software) advanced digital filters enabling the result to be stabilized in particularly difficult and unstable measuring conditions. Running this function causes the partial values of measured insulation resistances to be filtered within user-selected time intervals.

Insulation resistance measurement is not the only feature of the new meters. They are also capable of step voltage insulation resistance measurement (SV). This gradually increases insulation exposure helping to disclose certain types of damage, such as moistening. Each series of SV measurements comprises consecutive tests carried out within a pre-set time with a stepwise increasing voltage, for example: 1 kV → 2 kV → 3 kV → 4 kV → 5 kV. After the series of measurements has finished, all the results for individual voltages are saved in the memory.

Another function is the measurement of Dielectric Discharge ratio (DD) - an insulation condition indicator independent of test voltage. DD indicator allows for the assessment of the deterioration (ageing) of insulation parameters and detects moisture or delamination. The measuring procedure consists in charging an object (as during the measurement of insulation resistance), and then, after discharging the object for 60 s, measuring the discharge current. The charge stored in the dielectric can be measured in this way. The obtained result helps to evaluate the condition of the insulation.

Measurement limits (limiting values) can be set when measuring insulation resistance or continuity with a MIC-5010 meter. After the measurement, the display shows an additional message indicating whether the pre-set limit was exceeded or not. Information about the pre-set limit and the test result is saved in the meter's memory together with the measurement result.

Measuring capabilities of the devices include:

low-voltage continuity measurement of protective connections and equipotential bonding with current ≥200 mA, while using cables of any length (MIC-5010);
memory capacity of up to 11880 records - can store 990 results of any kind of measurement; wireless or USB cable data transmission to a PC; data transfer software (and the option to supplement the set by software to create Sonel PE-5 protocols);
power supply from a high-capacity battery and built-in charger of optimum charging rate depending on the degree of battery discharge.