LTR51 Carrier-board module - frequency meter and time interval meter

Carrier-board module - frequency meter and time interval meter
  • Specialized module for measuring the frequency, the period of complex-shape signals and counting pulses.
  • Separate setting of the upper and lower levels of the input two-threshold comparators for each channel allows to exclude the "chattering effect" during the hardware allocation of a discrete signal from complex-shape signal.

This module with a configurable number of measuring channels is designed as a carrier for the installation of two-channel measuring submodules H-51FH or H-51FL; the number of input channels is determined by the number of installed submodules.

Each parallel measuring channel has a separately configurable two-threshold input signal selection circuit.

Selection ranges ±10 V and ±1.2 V are determined by the setting of jumpers, and the trigger levels within the ranges are set programmatically - up to 256 levels.

LTR51 module can be used for multichannel measurement of frequency, period, number of pulses on pulse outputs of various instruments and sensors (meters, flowmeters, shaft speed sensors, etc.) and analog outputs (4/20 mA, 0/5 B, etc.) of devices, in which a binary counting signal of frequency can be extracted at a predetermined level.

Number of channels 2, 4, 6, …. 16 (independently adjustable, with parallel polling, is determined by the configuration of submodules)
Number of submodules From 1 to 8 (H-51FH or H-51FL)
Type of inputs Single-phase (with "common ground")
Input signal range ±10 V
The maximum allowable range of input signal (input protection) ±18 V when ON
±5 V when OFF
Input impedance, measured at zero frequency, not less than 100 kOhms when ON
1 kOhms when OFF
Maximum sampling frequency of input signal 500 kHz
Maximum possible measurement frequency 250 kHz (is equal to half the sampling frequency)
Resolution when measuring the pulse width 2 μs (is equal to the sampling rate period)
Maximum measured pulse width and minimum measured frequency It is not fundamentally unlimited (defined by top-level software)
Accuracy of measuring the period and duration of the pulse It is determined by the set measuring period and the error of setting the frequency of LTR crate reference generator (typically ±5*10-5 )
Scheme of selection (comparison) of the input signal Two-threshold with hysteresis, with programmatically controlled hysteresis thresholds
Voltage ranges of the comparison thresholds (set by setting the jumpers on the submodules H-51, see the notes below the table) -10,2 V… +10,1 V
-1,22 V… +1,21 V
Accuracy of setting the comparison thresholds 1.5% of the range of the comparison thresholds
Step of setting the comparison thresholds 256 levels, programmable within the set range of the comparison
The temperature drift of the zero of the comparison threshold, reduced to the input
(determined by characteristics of the component parts and the circuitry of the device; is not specifically controlled)
25 μV/°C
Temperature dependence of the comparison threshold calibration scale
(determined by characteristics of the component parts and the circuitry of the device; is not specifically controlled)
100 ppm/°C
Galvanic isolation
See the main features of LTR modules
  • Installation of H-51x submodules is mandatory. Installation from 1 to 8 submodules is allowed.
  • The module with any number of submodules occupies one slot in the crate.
  • When ordering the LTR51 in conjunction with the LTR-U-1-4 or LTR-EU-2-5 crates, be sure to specify the required ranges for setting the comparison thresholds, since the permutation of the jumpers on the H-51x submodules is difficult in the LTR-U-1-4 or LTR- EU-2-5 because of the need to disassemble them.

External signals connector 

Hardware description, assignment and connection of signals is given in the User's Guide.


  • ltr51api.pdf (filesize: 790 817 bytes, date: 21.03.2007)

    LTR51 module. Programmer's Guide.

  • ltrapi_en.pdf (filesize: 604 618 bytes, date: 15.02.2018)

    Ltrapi basic library. Programmer's Guide.

  • ltr_cross_sdk_en.pdf (filesize: 551 553 bytes, date: 13.02.2018)

    Description of the software for Windows, Linux, FreeBSD and QNX.

  • ltr_en.pdf (filesize: 11 066 427 bytes, date: 25.12.2017)

    LTR modular DAQ system. User's Guide (revision 3.1.0).

    • General characteristics and principles of construction
    • Working with LTR crate
    • Overview of LTR crate architecture
    • LTR11 ADC module
    • LTR212 (M) strain measurements modules
    • LTR27 measuring module
    • LTR41, LTR42, LTR43 digital I/O and synchronization modules
    • LTR51 frequency meter module
    • LTR22 ADC module
    • LTR24 (-1, -2) ADC modules
    • LTR25 ADC module
    • LTR34 DAC module
    • LTR35 DAC module
    • LTR114 ADC module
    • LTR210 ADC module
    • LTR00 Dummy module
    • Low-level programming of LTR-EU crate
    • Specification
  • ltr_soft_getting_started_en.pdf (filesize: 269 974 bytes, date: 13.02.2018)

    Starting to work with DAQ system LTR. Questions about the software.

LGraph2 software package

  • (filesize: 26 786 707 bytes, date: 11.10.2021)

    LGraph2 is a free multi-channel data recorder for Windows. Version 2.35.20 provides the possibility of simultaneous data visualization and recording from the ADCs: L-502, L-780M, L-783, L-791, E-502, E14-140, E14-140M, E14-440, E-154, E20-10, LTR11, LTR114, LTR27, LTR212, LTR216, LTR22, LTR24, LTR25, LTR51. It requires an updated version of the LComp driver (from version 01.04.2010) and ltrserver (no lower than

Software for Windows

  • lcomp.exe (filesize: 6 342 216 bytes, date: 12.05.2021)

    Beta version. LCOMP library for Windows XP/Vista/Win7/Win8/Win10 32 and 64-bit versions with drivers. The installer and drivers are digitally signed. The library is built on the basis of modern WDM-drivers rewritten on WDF. It includes the WDM driver itself for L-CARD hardware, the DLL library with source code, programming examples, electronic description, etc. The LCOMP library provides support for almost the entire range of products: PCI boards, USB modules. ISA support is excluded.

    The library includes “L-Graph I” software. L-Graph I supports the following devices: L-1450, L-761, L-780, L-783, L-791, E14-140, E-154 and E14-440. Files recorded by L-Graph I can also be read and processed using the demo-version of PowerGraph v.3.X.

  • ltrd-setup.exe (filesize: 1 467 408 bytes, date: 19.08.2021)

    The ltrd service. Version Provides communication with LTR crates. It is a replacement for the LTRserver software while maintaining the compatibility of the program interface. ltrd is designed for the same purpose as LTRserver, but it is a service that runs when the system is started. The graphical interface to the service is provided by a separate LTR Manager program.

    Attention! Only one of the programs ltrd or LTRserver can work at a time.

  • ltrdll.exe (filesize: 1 328 600 bytes, date: 30.11.2021)

    Libraries for working with LTR crates and modules. Version 1.32.30.

  • ltrmanager_setup.exe (filesize: 9 751 808 bytes, date: 04.05.2021)

    LTR Manager software. Version 1.5.2. Graphical interface to the ltrd service. Provides an interface similar to the LTRserver interface when working through the ltrd service.


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