HITACHI EH-150 PLC in depth analysis: characteristics, instructions, and system design

HITACHI EH-150 PLC in depth analysis: characteristics, instructions, and system design

Overview

The Hitachi EH-150 series is a compact and powerful modular programmable logic controller (PLC) designed to meet a wide range of industrial automation needs. This series of controllers not only inherits the software assets of Hitachi H-series PLCs, ensuring program portability, but also significantly expands performance and functionality, integrating 32-bit RISC processors to achieve high-speed and precise control.

The design concept of EH-150 emphasizes achieving maximum efficiency in a limited space, and its standard I/O module integrates pluggable terminal blocks and LED status indicator lights, greatly facilitating wiring and on-site diagnosis. The system supports DIN rail installation, with a sturdy structure that adapts to harsh industrial environments. As an important member of the H-series family, EH-150 not only provides a seamless upgrade path for existing H-series users, but also builds a highly scalable control system platform for new users.

System architecture and core features

2.1 Modular Hardware Structure

The EH-150 adopts a typical modular structure, and the core components of the system include:

CPU module: The "brain" of the system, responsible for executing user programs, performing logical operations, and I/O control. Different models, such as EH-CPU104A and the high-performance EH-CPU548, offer program capacities ranging from 3.5k steps to 48.5k steps, as well as basic instruction execution speeds from 1.0 μ s to 0.1 μ s, to adapt to application scenarios of different complexities. High performance CPUs (such as EH-CPU516/548) support up to 4 expansion boards and up to 3520 I/O points.

Power module: provides stable operating voltage for the system. Supports AC 100-240V wide range input (EH-PSA) or DC 24V input (EH-PSD).

I/O modules: including digital input/output (such as EH-XD series, EH-YT series), analog input/output (such as EH-AX series, EH-AY series), temperature detection (EH-PT4), high-speed counting (EH-CU), positioning control (EH-POS) and other modules, to meet the requirements of on-site signal acquisition and driving.

Base board and expansion cable: The base board is used to install CPUs, power supplies, and I/O modules, while the expansion board can greatly expand the system's I/O capacity through I/O controllers and dedicated cables. For example, using EH-CPU548 in conjunction with EH-BS11A 11 slot substrate can achieve a massive system configuration of up to 5 substrates and 55 slots.

2.2 Advanced Communication Capability

The EH-150 performs well in communication and provides a high degree of flexibility:

Dual standard communication ports: The CPU module comes standard with two communication serial ports (Port 1 and Port 2). Port 1 can be configured as a universal port through DIP switches and special internal outputs, supporting RS-232C, RS-422/RS-485 interfaces, and even built-in terminal resistors, making it easy to build a 1: N small data link system.

Built in modem interface: Specific CPU models (such as EH-CPU308 (A) and above) support connecting a modem on port 1 to monitor and maintain remote systems through the public telephone network.

Network module support: By extending the communication module, EH-150 can access various industrial networks, including Ethernet (EH-ETH), DeviceNet (EH-RMD/EH-IOCD), and PROFIBUS-DP (EH-RMP/EH-IOCP), enabling seamless integration into complex factory network architectures.

2.3 Data Security and Reliability

Battery free program maintenance: User programs are stored in the built-in FLASH memory of the CPU module, and even if the battery is depleted or not installed, the program will not be lost, greatly improving the reliability of the system.

Real time clock and logging function: Most CPU models (except EH-CPU104 (A)) have a built-in real-time clock that can timestamp events. Combined with EH-MEMD memory board, the system supports data logging function, which can record the historical data of designated data areas for process analysis and fault tracing.

Rich self diagnostic functions: The CPU module continuously performs self diagnostic tests, including memory checks, I/O configuration verification, program syntax checks, and watchdog timer monitoring. When an error is detected, an alarm will be triggered through the ERR LED indicator and a detailed error code from the special internal output (WRF000).

Powerful instruction system

The EH-150 has a rich instruction system, based on the H-series ladder diagram/instruction language, providing users with great flexibility in programming. Instructions are mainly divided into the following categories:

3.1 Basic Instructions

This includes basic touch commands (LD, AND, OR), output commands (OUT, SET, RES), and edge detection commands (DIF, DFN). These are the foundations of any ladder diagram program.

3.2 Timer and Counter

The system provides various timers and counters:

Timer: including traditional turn-on delay timer (TD) and newly extended TM timer. The number of TM timers is as high as 2048, and each timer can independently select a 0.01s, 0.1s, or 1s time base. The accumulator value range is from 0 to 65535, greatly enhancing the flexibility of timing tasks.

Counter: Supports regular counter (CU), ring counter (RCU), and up/down counter (CTU/CTD). The numbering space of all counters and timers partially overlaps (the first 256 points), so be careful to avoid conflicts when using them.

3.3 Application and operation instructions

Arithmetic operations: Supports four arithmetic operations of binary and BCD codes, logical operations (AND, OR, XOR), and data comparison (=,<>,<,>, etc.).

Data processing: Provides powerful block manipulation instructions such as block transfer (MOV), block copy (COPY), block swap (XCG), and shift/loop shift instructions (SHR, ROR) to facilitate the processing of large amounts of data.

Special function instructions:

PID control (FUN 0-2): In EH-CPU308 (A) and above models, PID operation can be achieved through dedicated instructions without the need for additional hardware modules. It can directly control analog I/O and achieve closed-loop control of process variables such as temperature and flow rate.

Communication command (TRNS0/RECV0): allows user programs to control the universal serial port for custom protocol communication with external devices such as printers, barcode scanners, or frequency converters.

Frequency converter control (FUN 190): specifically designed to control Hitachi SJ300/L300P series frequency converters through RS-485 interface, simplifying the programming of motor control systems.

ASCII/BIN Conversion Instructions: Provides a rich instruction set (such as BINDA, BINHA, ASC, HEX) for converting binary data and various formats of ASCII code, which is crucial for communication with smart instruments, HMI, and other devices.

3.4 Program Control Instructions

Jump and Loop: Program conditional jump is implemented through JMP/CJMP instructions, and program loops are constructed using FOR/NEXT instructions to effectively manage program flow and scanning time.

Subroutine calling: Use CAL instructions to call subroutines defined by SB and RTS, achieving modular programming.

Interrupt program: The INT0-INT3 instructions allow the creation of interrupt programs with periodic execution (cycles of 5ms, 10ms, 20ms, 40ms), used to handle tasks with strict time requirements. The manual specifically states that for a 5ms cycle scan, the program execution time must be strictly controlled to avoid "overload errors" caused by execution timeouts.

Programming and System Operations

4.1 Programming Environment

EH-150 mainly uses Hitachi's dedicated LADDER EDITOR for Windows ®  Software programming. This software supports offline programming, online monitoring, and debugging. When programming, it is necessary to correctly configure the CPU type (choose EH-150 or backward compatible H-302) and memory capacity.

4.2 Scanning cycle and system processing time

EH-150 operates in a periodic scanning mode. A complete scanning cycle includes system processing (such as refreshing timers, communicating with peripheral devices) and user program execution.

Variable system processing time: For enhanced CPUs (EH-CPU * * * A/448/516/548), the system processing time can be adjusted between 1ms and 8ms through a special internal output WRF038. The default value is 2ms, which increases the proportion of user program execution time and can shorten the scanning cycle.

Overload error: When the execution time of a scan exceeds the set overload check time, the system will trigger an overload error. Users can choose whether to continue running during overload through special internal outputs (R7C0, R7C1).

4.3 Program modifications during RUN

EH-150 supports program modification in RUN state, greatly improving the convenience of system debugging and maintenance. When performing "online modification", the CPU will briefly pause (HALT time), complete program modification and verification, and start executing the new program from the next scanning cycle. The modified program will eventually be written into the FLASH backup memory. During this process, the special internal output R7EF will remain in the ON state, reminding users not to cut off the power during this period to prevent program damage.

Safety regulations and fault handling

The manual emphasizes strict safety regulations at the beginning, dividing safety precautions into two levels: "danger" and "caution", accompanied by illustrations.

Installation and wiring:

Environmental requirements: It must be used in the specified environment (temperature, humidity, non corrosive gas).

Grounding requirements: Reliable functional grounding (FE) must be carried out to prevent electric shock and malfunctions.

Emergency stop and interlock: Emphasize that the emergency stop circuit and interlock circuit must be built outside the PLC to ensure equipment safety even if the PLC itself fails. Special warning: External load interlocking should not be achieved by controlling the relay drive power supply of the relay output module.

Battery safety: It is strictly prohibited to reverse, charge, disassemble, heat or short-circuit the battery to prevent explosion or fire.

Fault diagnosis:

The system indicates different levels of errors (severe, moderate, minor, warning) through the combination of on/off/flashing of RUN and ERR LEDs on the CPU module.

The detailed error code is stored in the special internal output register WRF000. Users can monitor the register through programming software or clear error messages by setting the R7EC bit.

Chapter 14 of the manual provides a detailed troubleshooting checklist and flowchart, guiding users to systematically solve problems from power supply, CPU, I/O modules to peripheral devices.

Conclusion and Design Considerations

The Hitachi EH-150 series PLC, with its modular design, powerful processing capabilities, rich instruction set, and flexible communication options, has become a reliable solution suitable for mid to high end industrial control scenarios.

When designing a system, engineers should focus on the following points:

Selection matching: Select the appropriate CPU model (from economical CP104A to high-performance CP548) based on the number of I/O points, program complexity, and whether PID or positioning control functions are required.

Expansion planning: Reasonably plan the configuration of the basic substrate and expansion substrate, paying attention to the limitations of the CPU on the expansion substrate and I/O points.

Communication strategy: Select appropriate communication ports (dedicated/universal) and protocols (H-series protocol, Modbus RTU, etc.) based on the communication needs of devices such as the upper computer, frequency converter, HMI, etc.

Safety design: Strictly follow the safety specifications in the manual and build a reliable external safety circuit.

Code optimization: Reasonably use interrupts, subroutines, and jump instructions, control scan cycles, and avoid overload errors.

By gaining a deep understanding of the system architecture and instruction details of EH-150, developers can fully utilize its potential to build efficient, stable, and secure automation control systems.