LPW25 Voltage and current transducers

Voltage and current transducers
  • 2-channel LPW25-U-2 for voltage measurement relative to the ground terminal
  • 1-channel LPW25-I-1 for measuring the amperage in phase or neutral circuit
  • Connections to LTR24-2 or LTR25 by cable with maximum possible length of tens meters
  • Any combination of the required number of current and voltage measurement channels for measurements in single-phase and multi-phase AC networks
  • Mounting on DIN rail

2-channel LPW25-U-2 transducers are designed to measure the voltage relative to the ground terminal in AC power networks up to ~ 0.4 kV (and also higher voltage when using external voltage transformers). Phase, linear voltages in the 3-phase network can be calculated from the measurement results obtained by two LPW25-U-2 transducers which measures 2 corresponding voltages relative to the ground terminal.

Single-channel LPW25-I-1 transducers are designed to measure current up to 5 A in electrical networks with voltages up to ~ 0.4 kV AC (and also higher current or voltage when using external current transformers).

LPW25 transducers are used in conjunction with LTR24-2 or LTR25 modules to create an AC measuring system with continuous data acquisition with the ability to calculate the values of electric quantities (amplitude, phase, power, energy) and obtain oscillograms and spectrograms. The main applications of the LPW25 (in conjunction with LTR24-2 or LTR25): the study of transients in power networks in the frequency range from 10 to 10,000 Hz.

LPW25 transducer interface is compatible with the IEEE 1451.4 standard and is a 2-wire interface for each transducer channel with DC power supply and delivery of the transducer output (alternating voltage component) via the same 2-wire interface.


Designation of LPW25 transducers

General characteristics of LPW25

Number of measurement channels






Input measuring range 




400 V (AC line voltage)

5 A (AC power in the phase or neutral circuit)

Maximum voltage

- AC line voltage

- AC phase voltage


800 V

460 V

Maximum AC power  (LPW25-I-1-5) 10 A

The influence of the DC component of the current to the measurement error






The basic error, reduced to the measurement range of the AC voltage at a frequency of 50 Hz:





The basic error, reduced to the range of AC power measurement at a frequency of 50 Hz:






Bandwidth at -3 dB 10 to 10000 Hz
Input resistance (LPW25-U-2-400-1) relative to the ground terminal (2000±12) kOhm
Input impedance (LPW25-I-1-5)   Not more than 0.011 Ohm at a frequency of 50 Hz

Transducer's transfer ratio (see Note 1)




0,01 V/V

0,5 V/A

The amount of Flash memory of each transducer channel for recording calibration coefficients and identification information 1 Kbit

Note 1. Reference characteristics of the transducer's transfer ratio are given. Actual transfer ratio are indicated in the transducer passport and written to its flash memory. The program function of reading flash-memory of LPW25 transducers is announced in new versions of LTR25 modules.


Typical LPW25 connection in a 3-phase measuring system 0,4 kV, 5 A


Note 2. Cable length limitation from LPW25 to LTR is affected by the resistance of the wires, the cable capacity and the requirement of the upper frequency of the passband. These restrictions are similar to the limitations of the ICP interface.


External voltage and current transformers connecting to LPW25

To implement a voltage measuring range greater than 0.4 kV (linear) and a current of more than 5 A, external voltage transformers (VT) and current transformers (CT), respectively, should be used. The primary windings of VT and CT must be included in the measured circuits, and secondary (II) - connected to the LPW25 according to the schemes shown in the figure below. When the CT is connected, the K-coupler must be used to safely disconnect the LPW25 if necessary.




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Fax: +7 (495) 785-95-14

Sales department: en@lcard.ru
Technical support: en@lcard.ru

5 Varshavskoye shosse, corp. 4, build. 2
Moscow 117105
Russian Federation

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