UM344-2

CIRCUIT DESCRIPTION

The current from the 104 microamp source is applied to the RTDI(+) pin which is jumpered to the TC(+) pin. Since the 52 μA sink network draws 52 microamps, the remaining current flows through the RTD input to ground creating a voltage at the input to the 2-pole filter. 52 microamps is drawn through the TC

(+)pin into the 52 μA sink network, ensuring that when a 3-wire RTD is used , both measurement leads will have identical current flowing in the same direction into the transmitter.

7.2.3 Signal Conversion

The digitized sensor and reference junction signals are passed from the input circuit’s A/D Converter through isolated pulse transformers into the microcontroller (μC) for signal linearization and temperature compensation.

The output signal from the μC is applied to a D/A Converter which outputs two variable width pulses (PULSE ON/PULSE OFF). The widths of the pulses are modulated in direct proportion to the voltage level of the sensor input signal. The pulses are simultaneously applied to the V/I Converter and to two P- channel FETs within the Converter. The output from the FETs is filtered and fed into an operational amplifier whose output drives the voltage-to-current conversion circuit, a Darlington transistor pair acting as a pass transistor for the 4 to 20 mA loop current output.

7.2.4 Communication Format

The Model 344 communicates, via the HART protocol, with the portable MXC and any Primary or Secondary Master connected to the Network.

HART communication uses phase-continuous frequency-shift-keying (FSK) at 1200 bits/sec and frequencies of 1200 Hz for logic 1 and 2200 Hz for logic 0. HART communications are superimposed (AC coupled) on the analog 4-20 mA signal. Because the digital signaling is high frequency AC, its DC average is zero and does not interfere with analog signaling.

A 2-Pole Active Filter connected to the loop input receives HART transmissions. The filter rejects low frequency analog signaling, and other out-of-band interference, preventing a compromise of the digital reception. The filtered signal is applied to a Zero Crossing Detector which converts the filtered information into clean pulses of uniform amplitude before introduction to the Bell 202 Modem.

The Modem receives and processes (e.g., demodulation) the serial FSK signal (Rxa) and outputs the signal (Rxd) to the Microcontroller where serial to parallel conversion is performed.

In response to the received signal, the Microcontroller outputs a signal (Txd) to the Modem where it is modulated and fed into the feedback circuit of the V/I Converter for transmission (Txa) over the loop.

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September 1995

7-5

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Siemens UM344-2 user manual Signal Conversion, Communication Format
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UM344-2 specifications

The Siemens UM344-2 is a cutting-edge industrial controller designed to meet the demands of modern automation and control systems. This powerful device is specifically developed for use in various applications, including manufacturing, process control, and machinery integration. The UM344-2 stands out for its versatility and robust performance in harsh industrial environments.

One of the main features of the Siemens UM344-2 is its high processing speed, which allows for real-time data processing and decision-making. The controller utilizes advanced microprocessor technology, ensuring quick response times and efficient operation. Its architecture supports multitasking, enabling it to manage multiple processes simultaneously without compromising performance.

The UM344-2 features a modular design, which provides flexibility in configuration and scalability. Users can easily add or remove modules to tailor the system to specific application requirements. This adaptability is beneficial for businesses that need to scale their operations or adjust to changing production demands. The controller is compatible with a variety of I/O modules, allowing for seamless integration with other equipment and systems.

In terms of connectivity, the Siemens UM344-2 supports various communication protocols, including Profibus, Profinet, and Ethernet. This versatility ensures smooth data exchange between the controller and other devices in the automation ecosystem, facilitating comprehensive monitoring and control. The inclusion of these communication standards enhances interoperability and allows for the integration of legacy systems with newer technology.

The Siemens UM344-2 is equipped with advanced diagnostic tools, which enable users to monitor system performance and detect potential issues in real-time. This feature reduces downtime and maintenance costs by allowing for proactive management of the system. The controller also supports remote access capabilities, enabling technicians to troubleshoot and configure systems from off-site locations.

Safety is a critical consideration in industrial environments, and the UM344-2 is designed with this in mind. It incorporates safety-certified features, ensuring compliance with international safety standards. Users can implement safety functions directly within the controller, streamlining system design and reducing the need for external safety components.

Overall, the Siemens UM344-2 exemplifies the fusion of technology and practical application, making it an essential component for businesses looking to enhance their automation processes. With its high performance, flexibility, and focus on safety, the UM344-2 is a reliable choice for industries aiming for efficiency and innovation in their operations.
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