IC693ALG392 4 to 20 mA output signal module

Description

The IC693ALG392 is a Series 90-30 module. This module is an analog output module that is typically used for implementing modulating control of instruments or devices such as Variable Frequency Drives (VFD), Control Valves, Positioners, converters and other similar modulating devices. It may also be used to re-transmit analog data to receiving elements such as recorders, data loggers and other compatible receiving devices.

The IC693ALG392 features Eight (8) output channels with configurable resolution of 15 or 16 bits, depending on the analog output range selected. It is capable of providing voltage signals such as 0 to +10 volts (unipolar) / -10 to +10 volts (bipolar) voltage and 0 to 20 milliamps / 4 to 20 milliamps output signals. In able to generate the output analog signals, this module requires an isolated 24VDC power, directly connected to the designated terminal block of the module.

This module is factory calibrated. Calibration information includes .625 µA for 0 to 20 mA; 0.5 µA for 4 to 20 mA; and .3125 mV for voltage (per count). Each channel of the module exhibits an update rate of Eight (8) milliseconds with resolution of 0.5 µA (1 LSB = 0.5 µA) for 4-20 mA; 0.625 µA (1 LSB = 0.625 µA) for 0-20 mA; 0.3125 mV (1 LSB = 0.3125 mV) for 0-10VDC and 0.3125 mV (1 LSB = 0.3125 mV) for -10 to +10VDC outputs signals.

With the continuous improvement of automation level in thermal power generation units, the functional range of unit unit DCS system continues to expand. In the past two years, the unit control room of newly built and renovated units has relied on DCS for all operations except for backup manual operations for emergency shutdowns and boiler shutdowns. Therefore, the phenomenon of tripping caused by DCS faults often occurs. So, how to improve the reliability of DCS has become an important topic in front of everyone engaged in thermal automation work. Due to work relationships, I have had the opportunity to collect funds, communicate, or inspect more than thirty thermal power plants, and have been exposed to nearly eighty 100~700MW unit units that have applied DCS, covering almost all types of DCS used in China. I have a good understanding of the faults that occur in various types of DCS, whether it is imported DCS or domestic DCS. Although the principles and structures are completely different, the subsystems involved are also different, But similar faults have occurred to some extent. Through in-depth and detailed analysis of typical faults, the true cause of the faults can be identified, and preventive measures can be formulated and implemented correctly, which can effectively prevent the recurrence of such DCS faults.

This article lists several typical DCS fault cases for reference by personnel engaged in thermal technology management and maintenance.
Case 1: Controller restart causing unit trip
On November 1, 2001, before the shutdown of Unit 4 in A Power Plant, the active load was 270MW and the reactive power was 96MVar. The A and B excitation regulators automatically operated in parallel, with manual 50Hz cabinet tracking for backup. At 14:26, the accident sound was emitted, the generator outlet switch and excitation switch tripped, and alarm signals such as “regulator A cabinet exited operation” and “regulator B cabinet exited operation” were issued, and the unit was disconnected. Upon inspection and testing of the ECS control system, it was found that the # 14 controller had malfunctioned and was offline. The redundant # 34 controller was restarted. After replacing the main boards of the # 14 and # 34 controllers, the unit was restarted. Shortly after, the generator transformer unit was paralleled with the system.
Cause analysis: Based on the analysis of historical data, at 13:31, the # 14 controller hardware malfunctioned and went offline.

The hot standby # 34 controller was automatically switched from auxiliary control to main control. At 14:26, the # 34 controller misjudged “WATCHDOG” due to communication congestion, causing the controller to restart. Due to the long signal control method of the excitation regulator by the controller and the lack of breakpoint protection function, the # 34 controller cannot automatically return to the state before the breakpoint after restarting, causing the A and B regulators to automatically exit operation and the manual 50Hz cabinet to automatically switch on. Due to the loss of excitation of the generator, the voltage at the generator end decreased, resulting in a decrease in the voltage of the auxiliary power supply. The output voltage of the manual 50Hz cabinet continued to decrease. After the manual 50Hz cabinet was put into operation, the generator did not break out of the loss of excitation state until the excitation device was cut off, causing the generator loss of excitation protection action and the generator outlet switch to trip# The 14 controller and # 34 controller control the generator-transformer unit equipment, including the backup automatic switching relay contact BK for auxiliary power switching. After the # 34 controller restarts, BK automatically resets, the relay contact disconnects, and BK is switched to the exit position, resulting in unsuccessful automatic switching of the 6KV power switches 6410 and 6420.

Preventive measures
Replace the faulty controller. Later, the manufacturer confirmed that there were problems with this batch of motherboard crystal oscillators and agreed to replace them for free. They took advantage of the shutdown opportunity to replace all controller motherboards of Unit 4.
Add offline alarm function for any controller, I/O card, or communication card.
The internal time setting of “WATCHDOG” in the program is too short, which can easily cause misjudgment and require software upgrades for all controllers.

Add breakpoint protection function to the configuration diagram of the AQK and BQK mode switches of the regulator and the automatic switching BK switch of the auxiliary power backup to prevent the excitation regulator and the automatic switching switch of the auxiliary power from exiting operation after the controller starts automatically.

Check all configurations of the ECS system and modify the logic that has the above issues.

Contact the regulator manufacturer to ensure that the regulator can maintain its operating state internally. Change the way the controller controls the regulator to short pulse signal control.

Add manual 50Hz cabinet output voltage automatic tracking function in ECS.