Polarization index testers
A PI tester (polarization index tester) is a specialized insulation measuring device that can be used to reliably assess the condition of electrical insulation, particularly in motors, generators, transformers, and other high-voltage systems.
The device according to the polarization index method, in which the insulation capacity is measured and analyzed over a defined period of time. The insulation resistance is recorded insulation resistance several points in time, typically after one and ten minutes, and the PI value is calculated from the ratio of these values.
In order to assess the condition over longer periods of time, measurements can be taken at regular intervals, for example quarterly, semi-annually, or annually. If the PI value decreases over time, it is advisable to shorten the test intervals in order to be able to react to possible insulation damage at an early stage.
The PI value is a reliable indicator for:
- Moisture in the insulation
- Contamination or aging
- surface conductivity
Key facts:
- Meaningful assessment of insulation quality
- Temperature-independent evaluation
- Early detection of moisture, contamination, or aging
- Ideal for preventive maintenance and condition monitoring
- Automated measurement sequences with integrated PI calculation
MotorAnalyzer1
The entry-level model for your engine service
CHECK YOUR MOTORHEALTH!
For electrical machine manufacturers
For electric motor repair
For maintenance, servicing, and repair
• Asynchronous, synchronous, and DC machines, brakes, transformers, coils, etc.
• Troubleshooting and fault location
•PI and DAR testing – testing the condition of motors
• And much more...
• Lightweight and portable
• Off-grid operation
• PC software for printing and Save
MotorAnalyzer3
The mobile ALL-IN-ONE professional model for your engine service
CHECK YOUR MOTORHEALTH!
For electrical machine manufacturers
For electric motor repair
For maintenance, servicing, and repair
Essential testing methods
- surge test 3 kV
- Resistance test
- Insulation resistance test – 6 kV
- high voltage test – 6 kV
- Polarization index, DAR – 6 kV
- inductance
- impedance
- Capacitance
- turn-to-turn fault localization probe
- AdjustmentNeutral Zone
- sense of rotation sense of rotation
- …
- Off-grid operation
- PC software for printing and Save
- Communication with
PC via Bluetooth
MTC2 R7
Universal winding testers from 6 to 50 kV
For production, EOL, automation
For testing laboratories, R&D, approval, certification testing
For repair, maintenance, and service
- stator sense of rotation a measuring probe in stator .
- Determine rotating field manually rotating the motor shaft.
Surge test
- Ultra-fast 50 measurements per second
- Phase comparison between each other
- Patented peak-to-peak measurement
Partial discharge during surge test DIN EN 60034-18:2014
- Passive or active antenna
- Wired decoupling
ohmic resistance
- winding
- temperature sensor
insulation resistance
- IR
- PI, DAR
High voltage AC optional
test connections
- Standard: 4
- Optional: 7 and more
Good to know:
The polarization index test
A PI tester is used to precisely evaluate the insulation quality of electrical machines, such as motors, generators, or transformers. It measures the polarization index (PI), a characteristic value that provides information about the condition of the insulation.
Functionality
- measurement principle
The testing device generates a constant DC voltage (usually 500 V to 5 kV) and measures the insulation resistances after 1 minute (R₁) and 10 minutes (R₁₀).
- calculation
- The PI value is calculated from the ratio R₁₀/R₁.
Interpretation of values
|
PI value |
Statement on isolation* |
|
< 1,0 |
Critical – severe impairment |
|
1.0–2.0 |
Borderline – further analysis recommended – action is required |
|
2.0–4.0 |
Good – insulation in decent condition |
|
> 4,0 |
Very good – dry, clean insulation |
* These are approximate values and are not guaranteed. Further specifications can be found in the relevant standards (e.g., IEEE 95-1977).
Long-term monitoring with PI testing
Regular PI measurements are recommended for assessing the condition of electrical insulation over longer periods of time—for example, annually, semi-annually, or quarterly.
If the PI value decreases over time, the test interval should be shortened in order to be able to react to possible insulation damage at an early stage.
If the PI value reaches a critical space, preventive maintenance measures may be advisable.
This helps to avoid unplanned downtime and allows maintenance or repair work to be scheduled during predictable time slots—for example, during company vacations or non-production phases.
Typical areas of application
- Maintenance and repair of electrical machinery
- Condition diagnosis prior to Commissioning
- Quality assurance in manufacturing
benefits
- More meaningful than individual measurements of insulation resistance
- Automated measurement sequences with integrated PI calculation
- Documentation and evaluation possible via interfaces
The SCHLEICH – Expect more!
Insulation, PI, and DAR testers
- TEST VOLTAGE 30 V up to 50,000 V DC
- Standard-compliant test voltage profiles over time
- Often in combination with other test methods such as high voltage DC/AC, step voltage measurement, surge test, partial discharge measurement, etc.
- Standardized interfaces such as RS 232, Ethernet/LAN, USB for PC communication
- 24 V digital I/O for PLC communication
- Expandable to Industrial Ethernet and fieldbus systems for PLC
- Virtually unlimited storage space for test plans and test results
- All parameters determined via the software
Customized testing devices and systems
- Single and combination test devices
- Testing machines/testing systems with relay matrix
(2, 3, 4, 6, 9, 12, 15, 18, 21 … 100 terminals) - Complete test workstations
- Production lines with transfer systems
- EOL workstations
- large-scale plants
full-service
- Professional advice with technical expertise
- Careful initial commissioning
- Regular certified calibration
- After-sales support from our service team
- Service by phone, remote maintenance, or on-site
- Customized training courses
- SCHLEICH.CARE.PREMIUM
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