LTR212M Specialized ADC module for strain measurements

Specialized ADC module for strain measurements

LTR212M is a specialized ADC module designed for direct connection and accurate measurement of voltage disbalance of bridge, half-bridge, quarter-bridge connection schemes of strain gauges or other resistive sensors.
The module is used in the composition of portable or multi-slots LTR crates and allows you to create a strain-measuring complexes with flexible channels configuration.

Specialized ADC module for connecting up to 8 strain gauges with a resistance from 100 Ohms to 1 kOhm (for sensors of 50 Ohm see the note below).

Up to 8 channels of sigma-delta ADC bridge imbalance measurement, 24 bits, with software-switchable millivoltage measurement subbands, analog input low-frequency filters and additional digital filtering with ADSP-2185M.

The source of the reference voltage (for supplying strain gages) with software-switchable output voltage +2.5 V or +5 V (constant or alternating) and total operating current load up to 400 m.

Built-in compensating DAC for each ADC channel for software-controlled hardware compensation of the initial unbalance of strain gages without reducing the dynamic range of the ADC.

The internal circuits of the extension to the full bridge when connected to external half-bridge or (for LTR212M-1) when connected to standard quarter-bridge sensors 200 or 350 Ohms. User has an opportunity to mount his own additional resistors to the removable submodule for LTR212M-1 with non-standard resistance of the external quarter-bridge sensor.

Note: It is possible to connect up to 8 strain gauges of 50 Ohm with a supply voltage of +2.5 V, or connect up to 4 strain gauges of 50 Ohm with a supply voltage of +5 V, but only in conjunction with LTR212, LTR212M-2 or LTR212M-3).

Fast commutation
of external signals
There are several holes in the board to fix a cable assembly.

37-pin interface terminal block board

DB-37F-increaser

ADC

Number of channels

4/8

Resolution

24 bits, sigma-delta ADC

Input signal measuring subranges

±80 mV, ±40 mV, ±20 mV, ±10 mV,
0…80 mV, 0…40 mV, 0…20 mV, 0…10 mV

Input impedance

Not less than 10 MOhm

Limits of the permissible basic relative error, in percents, without the use of "Calibration of zero" operation.

Notation in formulas: X_К is the final value of the set measurement subband, V; X - the value by LTR212M, V

	For subbands ± 80 mV, 0…80 mV, ± 40 mV
	For subbands 0…40 mV, ± 20 mV
	For subbands 0…20 mV, ± 10 mV, 0…10 mV

The range of common-mode voltages at the measuring inputs (to "AIN +" and "AIN-") relative to the supply point of the bridge "-EXC"

From +1,25 V to +3,75 V	When the supply voltage of the bridge is 5±0.2 V
From 1,25 V to 2,5 V	When the supply voltage of the bridge is 2.5±0.1 V

The coefficient of suppression of input common-mode interference when the unbalance of external input circuits resistances is equal to 1 kOhm

Not less than 100 dB

Supported connection schemes	LTR212	LTR212M-1	LTR212M-2	LTR212M-3
Up to 4 complete bridges in 4-channel mode on 4-wire or 6-wire scheme	+	+	+	+
Up to 8 complete bridges in 8-channel mode for 4-bit or partially 6-wire scheme	+	+	+	+
Up to 4 half-bridges in 4-channel mode by 3-wire scheme	+	+	+	+
Up to 4 half-bridges and 4 complete bridges in 8-channel mode by mixed scheme	+	+	+	+
Up to 4 quarter-bridges in 4-channel mode by 3-wire scheme	–	+	–	–
Up to 4 quarter-bridges and up to 4 complete bridges in 8-channel mode by mixed scheme	–	+	–	–

Reference voltage source (RVS)

Output voltage of RVS (sensor supply voltage)

(2.5 ± 0.1) V or (5 ± 0.2) V, the DC voltage or alternating current (programmable)

Maximum total load current

400 mA

Amplitude-frequency characteristics and parameters of the built-in digital filtering

Maximum sampling rate (for four-channel mode)

7600 Hz for each channel

Stability of the conversion frequency of one module (in new versions of LTR212M, the ADC conversion frequency is synchronized with the frequency of the LTR crate reference oscillator)

±50 ppm

Bandwidth of the signal transmission at -3 dB level with digital filtering disabled

2000 Hz

Digital tunable low-pass filter

Bandwidth transmission (the upper level is -3 dB)	Data output frequency
0...25 Hz	190,0 Hz
0...72 Hz	316,67 Hz
0...259 Hz	690,91 Hz
0...460 Hz	1085,71 Hz
0...680 Hz	1520,0 Hz

Galvanic isolation
See the main features of LTR modules

Differences between modifications

Consumer properties	LTR212	LTR212M-1	LTR212M-2	LTR212M-3
Synchronization of ADC conversion frequency with the frequency of the reference generator of LTR crate	–	+	+	+
Synchronous start of data acquisition with other LTR modules	–	+	+	+
Compatibility with old BIOS 1.1	+	–	–	+
Compatible with new BIOS 2.0	+	+	+	+
Compatibility with old top-level software at the API level	+	+	+	+
Nonvolatile memory	256 bytes EEPROM	0,5 MB, Flash-memory	0,5 MB, Flash-memory	256 bytes EEPROM
Calibration for 5 V RVS	+	+	+	+
Calibration for 2.5 V RVS	–	+	+	–
Test mode for creating a standardized unbalance of quarter-bridges	–	+	–	–
Option to connect up to 4 quarter-bridges in 4-channel mode via 3-wire connection scheme	–	+	–	–
Option to connect up to 4 quarter-bridges and up to 4 complete bridges in 8-channel mode via mixed connection scheme	–	+	–	–

Note: L-CARD recommends to switch from LTR212 to LTR212M-1, LTR212M-2, LTR212M-3 in new projects.

External signals connector

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

LTR212M-1

connection of up to 4 quarter-bridges, 4 half-bridges and 4/8 full bridges, 0.5 MB Flash memory, calibration for reference voltage source 2.5 V and 5 V
LTR212M-2

connection of up to 4 half-bridges and 4/8 full bridges, 0.5 MB Flash memory, calibration for reference voltage source 2.5 V and 5 V
LTR212M-3

connection of up to 4 half-bridges and 4/8 full bridges, 256 bytes EEPROM, calibration for reference voltage source 5 V

LTR212M-1

LTR212M-2

LTR212M-3

Descriptions

ltr212api_en.pdf (filesize: 630 826 bytes, date: 13.02.2018)
LTR212 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

lgraph2.zip (filesize: 26 783 707 bytes, date: 19.03.2021)
LGraph2 is a free multi-channel data recorder for Windows. Version 2.35.16 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 1.5.2.1).

Software for Windows

lcard-opc-setup.exe (filesize: 12 440 520 bytes, date: 09.04.2019)
OPC DA Server for L Card data acquisition modules and LTR crate system. Version 1.0.10.
lcomp.exe (filesize: 6 342 096 bytes, date: 20.01.2021)
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: 1 467 072 bytes, date: 25.11.2020)
The ltrd service. Version 2.1.8.6. 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: 1 293 128 bytes, date: 12.01.2021)
Libraries for working with LTR crates and modules. Version 1.32.22.
ltrmanager_setup.exe (filesize: 7 981 824 bytes, date: 25.11.2020)
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.