Digital automation instrumentation

A measurement amplifier with a bus interface acquires the typically very small analogue output signal from a load cell or strain-gauge-based sensor, conditions and amplifies the signal, and converts it into a digital measurement value. In this type of application, the device functions as a load cell amplifier, strain gauge amplifier and signal conditioner. The digital measurement value can then be transmitted directly to a PLC, industrial PC or other automation system via an industrial bus or communication interface.

The devices in this product group are primarily designed for load cells and other strain-gauge-based sensors with an mV/V output. These include force transducers and custom strain-gauge-based transducers. The sensor input signal, sensitivity and excitation requirements must be compatible with the respective load cell or strain gauge amplifier.

Depending on the model, serial interfaces such as RS232 and RS485 are available, as well as industrial communication systems including PROFIBUS DP, DeviceNet, CANopen, PROFINET IO, EtherNet/IP, Ethernet TCP/IP and Modbus TCP. RS485 also commonly supports Modbus RTU or the Laumas ASCII protocol.

Yes. Digital load cell transmitters, such as the LCB, are designed for this purpose. The analogue mV/V signal from an existing load cell is digitised close to the sensor and then transmitted via a digital interface. This often allows existing analogue load cells to remain in use when a machine or system is upgraded to modern digital communication.

When the load cell signal is digitised close to the sensor, the sensitive analogue mV/V signal only needs to travel over a short distance. Further transmission then takes place digitally via the fieldbus. This is particularly useful in larger installations, with longer cable runs, or when existing weighing systems are being upgraded for digital communication.

Yes, depending on the model. In addition to single-channel devices, multi-channel load cell amplifiers are available. The TLB4, for example, has four independent measurement channels, while the TLM8 series provides eight independent evaluation channels. Multi-channel systems can measure not only the total weight but also evaluate the signals from individual load cells separately, providing additional diagnostic possibilities.

In a conventional weighing system, multiple load cells are often connected in series before reaching the evaluation electronics. With a multichannel measurement amplifier, however, the signals from the individual load cells can be recorded separately.

This makes it possible, for example, to monitor load distribution and the operation of individual load cells. Faults or unusual loads can thus be detected more easily.

Yes, depending on the measurement amplifier. Various models provide an analogue output in addition to digital communication, for example 0–10 V or 0/4–20 mA. This allows the same measurement value to be transmitted digitally to the control system via a fieldbus while simultaneously being made available to other components as a conventional analogue standard signal.

OIML stands for the International Organization of Legal Metrology. Its recommendations define requirements for measuring instruments that are relevant, among other things, to weighing systems used for legal metrology. However, the product category alone does not determine whether an application is approved for legal-for-trade weighing. The specific OIML approval of the device must be checked, as well as whether the complete scale or weighing system meets the applicable legal requirements.

Yes. Various measurement amplifiers are designed for high-speed weighing and industrial automation. The LCB, for example, can calculate up to 500 weight values per second. With fast industrial networks such as PROFINET, EtherNet/IP or EtherCAT, measurement data can also be transmitted at high update rates. The speed actually required depends on the application. Static vessel weighing, for example, has different requirements from fast dosing, sorting or filling processes.

Yes. Direct communication with a PLC is one of the main applications of this product group. Depending on the control system, protocols such as Modbus RTU, PROFIBUS DP, PROFINET IO, EtherNet/IP, EtherCAT or another available communication protocol can be used. When selecting a measurement amplifier, it is therefore important to determine at an early stage which interface is supported by the existing PLC or automation system.

Digital measurement amplifiers combine signal conditioning and A/D conversion with direct communication to the automation system. Depending on the device, they can transmit not only measurement values but also status information, diagnostic data and device settings. This makes it easier to integrate multiple measurement amplifiers or load cell signal conditioners into networked machines and production systems.

Configuration depends on the specific model. Depending on the device, it can be carried out using operating buttons, a serial interface or PC software. The LCB, for example, provides a Micro-USB connection with dedicated configuration software. Parameters such as calibration, filters, inputs and outputs, and communication settings can be configured. Correct calibration of the measurement chain is particularly important for accurate load cell measurement.

The appropriate design depends on the installation location and environmental conditions. For control cabinets, compact load cell amplifiers and measurement amplifiers are available for DIN-rail or back-panel mounting. Other measurement amplifiers can be installed directly on or close to the load cell. For harsh industrial environments, versions with suitably protected enclosures are available. The LCB, for example, features a robust IP67 enclosure and can be mounted directly on the load cell body or on a wall.