Your local contact:Polarization Index Testers
A PI tester (Polarization Index Tester) is a specialized insulation testing device that can be used to reliably assess the condition of electrical insulation—particularly in motors, generators, transformers, and other high-voltage equipment.
The device operates using the polarization index method, in which insulation performance is measured and analyzed over a defined period of time. The insulation resistance is recorded at several time points—typically after one and ten minutes—and the PI value is calculated from the ratio of these values.
To assess the condition over longer periods of time, measurements can be taken at regular intervals, such as quarterly, semi-annually, or annually. If the PI value decreases over time, it is recommended to shorten the testing intervals in order to respond promptly to potential insulation damage.
The PI value is a reliable indicator of:
- 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 procedures with integrated PI calculation
MotorAnalyzer1
The entry-level model for your engine service
CHECK YOUR MOTOR'S HEALTH!
For electrical machine manufacturers
For electric motor repair
For maintenance, servicing, and support
• Asynchronous, synchronous, and DC motors, brakes, transformers, coils …
• Troubleshooting and fault location
•PI and DAR testing – Motor condition testing
• And much more …
• Lightweight and portable
• Battery-powered operation
• PC software for printing and saving
MotorAnalyzer3
The mobile all-in-one professional model for your engine service
CHECK YOUR MOTOR'S HEALTH!
For electrical machine manufacturers
For electric motor repair
For maintenance, servicing, and support
Key testing methods
- Surge Voltage Test – 3 kV
- Resistance test
- Insulation Resistance Test – 6 kV
- DC High-Voltage Test – 6 kV
- Polarization index, DAR – 6 kV
- Inductance
- impedance
- Capacity
- Coil end detection using a probe
- Adjustingthe Neutral Zone
- Direction of rotation
- …
- Off-grid operation
- PC software for printing and saving
- Communication with
«» PC via Bluetooth
MTC2 R7
Universal winding testers from 6 to 50 kV
For production, EOL, and automation
For test labs, R&D, approval, and regulatory testing
For repair, maintenance, and service
- Determine the direction of rotation using a measuring probe in the stator
- Determine the rotating field by manually rotating the motor shaft
peak voltage
- Ultra-fast 50 measurements per second
- Comparison of phases with one another
- Patented peak-to-peak measurement
Partial discharge under surge voltage in accordance with DIN EN 60034-18:2014
- Passive or active antenna
- Wired extraction
Ohmic resistance
- Winding
- temperature sensor
Insulation resistance
- IR
- PI, DAR
High-voltage AC (optional)
Test terminals
- Default: 4
- Optional: 7 or more
Good to know:
The Polarization Index Test
A PI tester is used to accurately assess the insulation quality of electrical machines—such as motors, generators, or transformers. It measures the so-called Polarization Index (PI), a parameter that provides insight into the condition of the insulation.
How it works
- Measurement principle
The tester generates a constant DC voltage (typically 500 V to 5 kV) and measures the insulation resistance after 1 minute (R₁) and 10 minutes (R₁₀)
- Calculation
- The PI value is calculated as the ratio of R₁₀ to R₁.
Interpretation of the values
|
PI value |
Statement on Isolation* |
|
< 1,0 |
Critical – severe impairment |
|
1.0–2.0 |
Borderline – further analysis recommended – action is needed |
|
2.0–4.0 |
Good – Insulation in good condition |
|
> 4,0 |
Very good – dry, clean insulation |
* These are approximate values and are provided without warranty. For further specifications, please refer to the relevant standards (e.g., IEEE 95-1977).
Long-term monitoring using PI testing
To assess the condition of electrical insulation over extended periods, regular PI measurements are recommended—for example, annually, semi-annually, or quarterly.
If the PI value decreases over time, the inspection interval should be shortened to allow for an early response to potential insulation damage.
If the PI value reaches a critical range, preventive maintenance may be advisable.
This helps prevent unplanned downtime and allows maintenance or repair work to be scheduled during specific, predictable time slots—such as during company holidays or periods when production is not taking place.
Typical applications
- Maintenance and Repair of Electrical Machines
- Pre-commissioning inspection
- Quality Assurance in Manufacturing
Advantages
- More informative than individual measurements of insulation resistance
- Automated measurement procedures with integrated PI calculation
- Documentation and analysis via interfaces are possible
The SCHLEICH Product Portfolio – Expect More!
Insulation, PI, and DAR testers
- Test voltage from 30 V to 50,000 V DC
- Standard-compliant test voltage waveforms over time
- Often used in combination with other testing methods such as DC/AC high-voltage testing, step-voltage testing, surge voltage testing, partial discharge testing, etc.
- Standard interfaces such as RS-232, Ethernet/LAN, and USB for communication with a PC
- 24 V digital I/O for PLC communication
- Expandable to Industrial Ethernet and fieldbus systems for PLC communication
- Virtually unlimited storage space for test plans and test results
- All parameters are set via the software
Custom testing equipment and systems
- Single-function and combination testers
- Automatic testers/test systems with a relay matrix
(2, 3, 4, 6, 9, 12, 15, 18, 21 … 100 terminals) - Complete testing stations
- Production lines with transfer systems
- EOL workstations
- Large-scale facilities
Comprehensive service
- Professional consulting backed by expert knowledge
- Careful initial startup
- Regular certified calibration
- After-sales support from our service team
- Service by phone, via remote support, or on-site
- Customized training programs
- SCHLEICH.CARE.PREMIUM
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