EJA is a well-known series of instruments produced by Yokogawa Electric Corporation in Japan. The EJA series includes pressure transmitters, differential pressure transmitters, level transmitters, and flow meters. Developed in 1994, this high-performance intelligent instrument utilizes advanced single-crystal silicon resonant sensor technology, which has gained widespread recognition for its reliability and precision.
The development of the EJA series received prestigious awards such as the Daehan Memorial Award in Japan and the Quality Product Award from Hashimoto Taro. It has also passed rigorous safety certifications in countries like the United States, the UK, France, Germany, Russia, and China. The EJA transmitters manufactured by Chongqing Company maintain the same quality standards as those produced in Japan, earning praise from users and meeting certification requirements for use in 200MW, 300MW, and 600MW power units.
This article explores the working principle of the EJA transmitter and provides key considerations for selecting the right model. Let’s dive into the details.
**Key Features of EJA Transmitter:**
1. The EJA transmitter is less affected by thermocouple effects, voltage drops, and temperature drift along the wire, allowing the use of cheaper and thinner cables, thus reducing installation costs.
2. Capacitive interference can cause errors in receiver resistance, especially in 4–20mA two-wire systems where the resistance is typically 250Ω. The EJA system allows for longer cable runs with minimal error.
3. EJA transmitters can easily integrate surge protection devices at the two-wire output port, enhancing safety against lightning strikes.
4. Each reading or recording device can switch between different channels without loss of accuracy due to wire length, enabling distributed data acquisition and centralized control. The 4 mA zero-level signal helps identify open circuits, short circuits, or sensor damage.
5. When the current source has sufficient output resistance, magnetic field-induced voltage in the loop has minimal impact. EJA transmitters can reduce interference using twisted pairs, while three- or four-wire systems require shielded cables with proper grounding.
**How Does the EJA Transmitter Work?**
The EJA transmitter converts differential pressure and pressure signals into frequency signals using two H-shaped vibrating beams on a single-crystal silicon resonant sensor. These signals are sent to a pulse counter, and the frequency difference is processed by the CPU. The signal is then converted via an analog-to-digital converter (ADC) to produce a 4–20mA output corresponding to the input signal. A BRAIN/HART digital signal is superimposed on the analog signal for communication.
The built-in correction memory in the bellows assembly stores ambient temperature, static pressure, and input/output correction data. This ensures excellent temperature and static pressure characteristics. Digital communication is possible through the I/O port with external devices such as handheld terminals (e.g., BT200, 275) or DCS cards. The BRAIN protocol uses 2.4 kHz, while the HART protocol uses 1.2 kHz, both superimposed on the 4–20mA signal without affecting it.
**Structure and Working Principle:**
1. **Sensor Structure:** The core of the single-crystal silicon resonant sensor is fabricated using micro-electro-mechanical systems (MEMS) technology. Two H-shaped beams are formed at the center and edge of the silicon chip, enclosed in a vacuum chamber to avoid air damping.
2. **Vibration Principle:** The silicon beam is placed in a magnetic field and forms a feedback loop with a transformer and amplifier, causing oscillation.
3. **Stress Conditions:** When pressure is applied to the top and bottom of the silicon wafer, it creates a pressure difference, leading to deformation. The central beam experiences compression, while the edge experiences tension, resulting in frequency changes that correspond to pressure variations.
**Performance Characteristics of EJA:**
- Excellent temperature influence performance
- Outstanding static pressure performance
- Strong one-way overvoltage protection
**EJX Series Overview:**
The EJX series features a high-quality electronic differential pressure transmitter with a single-crystal silicon sensor suitable for measuring flow, level, density, and pressure in liquids, gases, or vapors. It supports display of static pressure via an internal display or communication protocols like BRAIN or HART. Key features include fast response, remote protocol setting, self-diagnosis, optional alarm outputs, and compatibility with FF fieldbus. Standard configurations come with TUV certification, making them suitable for SIL2 applications (except FF fieldbus models).
**How to Choose the Right EJA Transmitter:**
1. **Pressure Range:** Determine the maximum pressure in your system. Select a transmitter with a range about 1.5 times larger than the maximum value to avoid sensor damage and ensure long-term stability.
2. **Medium Type:** Consider the properties of the measured medium. Corrosive or viscous substances may require special materials or chemical seals to protect the transmitter.
3. **Accuracy Requirements:** Define the required accuracy, including nonlinearity, hysteresis, repeatability, and temperature effects. Higher accuracy comes at a higher cost.
4. **Temperature Range:** Understand the operating and compensation temperature ranges to ensure consistent performance under varying conditions.
5. **Output Signal:** Choose between mV, V, mA, or frequency output based on distance, noise, and system requirements. For long-distance or noisy environments, mA or frequency output is preferred.
6. **Excitation Voltage:** Ensure the selected excitation voltage matches the transmitter's specifications, especially if the system requires stable power.
7. **Interchangeability:** Consider whether the transmitter can be used across multiple systems to simplify calibration and maintenance.
8. **Long-Term Stability:** Look for transmitters that maintain accuracy after prolonged operation to minimize future issues.
9. **Enclosure and Environment:** Choose a suitable enclosure based on environmental factors like humidity, vibration, and installation conditions.
10. **Connection Type:** Decide whether short or long-distance connections are needed, and consider the use of connectors if necessary.
11. **Special Requirements:** Confirm process connections, supply voltage, and additional needs like explosion-proof ratings or IP protection levels.
By carefully considering these factors, you can select the most appropriate EJA transmitter for your specific application, ensuring reliable and accurate performance.
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