By Ian Loudon, Omniflex Remote Monitoring Specialists.
Rate of change alarms are used to predict an event that is abnormal behaviour for a system or process, with the objective of taking preventive action in order to avoid system or process failure or damage. If a process value suddenly increases at a rate beyond the norm, then it indicates something unusual has changed in the system or process. This is different to an absolute (low or high) alarm.
Rate of change can be an increasing rate or decreasing rate. Using rate of change alarms also means you need to understand your process dynamics very well. You are taking expert knowledge and implementing it to safeguard your plant in the absence of the expert.
Rate of change alarms differ from normal (level) alarms in that they respond to a specified rate of signal change rather than to the crossing of an absolute threshold in the measured variable. A good example is a process variable that may or may not have a fixed alarm point but we need to predict when the trajectory of the process is going to harm the smooth running of the process or to prevent catastrophic failure and damage.
We also know that physical process parameters often over-shoot the desired limits, hence the use of process controllers using PID to manage this. However, in failure mode a process can still cause damage if the controller cannot respond to manage the process. Rate of change alarms will kick in only when the normal rate of change is exceeded. This pre-supposes that the normal rate of change is determined for a given process or system, often by an expert with intimate knowledge of the system.
Here are some examples of rate of change alarms and how an effective system design responds to them:
1. A reservoir that is emptying too quickly may need to trigger additional pumps into action to refill the reservoir. By predicting the low level before it happens, corrective action is taken before the low-level alarm triggers.
2. A sudden increase in the levels of a contaminant may need to trigger servicing of the system. The high level of contaminants can be predicted before they can cause damage, for example, gearbox oil contamination initiating a shorter service interval alert to pre-empt maintenance.
3. A rapid rate of temperature increase may indicate imminent damage or catastrophic failure before normal alarm limits are reached. Corrective action is taken before alarm limits are reached, possibly preventing motor winding damage.
Often the domain of control and safety software, rate of change alarms can be implemented in hardware. This has the advantage of adding an additional layer of protection to systems or processes. The Omniterm TTT from Omniflex, with its rate of change alarms option, provides just such an additional layer of plant protection.
A fresh approach to dairy processing VEGA Controls SA
Level Measurement & Control
Ensuring the quality and safety of milk throughout the production process is of the utmost importance in the dairy industry. The VEGABAR pressure transmitters are suitable for hygienic applications. They are an asset in the dairy industry and have been used with success for measuring the milk level and the process pressure in storage tanks.
Read more...Improved networking technology for fire and gas detection Omniflex Remote Monitoring Specialists
Fieldbus & Industrial Networking
Critical alarm and event management technology supplier, Omniflex has worked with the South African Nuclear Energy Corporation to upgrade equipment providing digital and analogue signals for its safety critical fire and gas alarm systems.
Read more...Simple and efficient level measurement in the mining, minerals and metals industries Endress+Hauser South Africa
Editor's Choice Level Measurement & Control
Measuring devices in the mining, minerals and metals industries face the challenge of varying material states and long distances in measurement height. Endress+Hauser’s answer to these challenges is the new Micropilot family.
Read more...Level measurement of an acid dosing tank at a WWTP
Level Measurement & Control
Ferric chloride and other acids are essential chemical substances in water and wastewater treatment. To control the dosing of acid solutions, an Australian wastewater treatment plant uses a special container to store, mix and add these chemicals. The company opted in favour of KROHNE’s OPTIWAVE 1540 radar level transmitter
Read more...Novel closed-loop CP technology for corrosion control Omniflex Remote Monitoring Specialists
Industrial Wireless
Cathodic protection specialist, Omniflex has collaborated with researchers at Deakin University to develop corrosion monitoring electronics for a novel closed-loop cathodic protection system for localised corrosion control in challenging industrial environments.
Read more...Powering sub-Saharan Africa’s energy future VEGA Controls SA
Level Measurement & Control
Crude oil storage plays an important role in the energy infrastructure of sub-Saharan Africa. The management of crude oil storage in comes with numerous challenges, including safety concerns, environmental conditions and infrastructural limitations.
Read more...How industrial network design impacts ESG commitments Omniflex Remote Monitoring Specialists
Fieldbus & Industrial Networking
In safety-critical industries like nuclear, petrochemical and oil and gas, installing a new industrial cable network is an extremely complicated task. Gary Bradshaw, a director of industrial network specialist, Omniflex explains why this is often unnecessary as plants are likely to have existing cabling capable of being used to create new industrial networks.
Read more...How CP system design can support ESG commitments Omniflex Remote Monitoring Specialists
Industrial Wireless
Major infrastructure like wharves, bridges, pipelines and tanks are under constant threat of corrosion, which can render them unsafe. David Celine, managing director of cathodic protection specialist, Omniflex explains how CP system design can support ESG commitments while simultaneously lowering costs and improving maintenance capabilities.
Read more...Level measurement of leachate from sewage sludge humification
Level Measurement & Control
A municipal utility in eastern Germany operates a state-of-the-art wastewater treatment plant with sustainable sludge treatment. The ultrasonic signal was being partially deflected by the wind, leading to frequent false measurements and inefficient process workflows. The problem was solved by replaced the ultrasonic level sensor with KROHNE’s OPTIWAVE 1540 non-contact radar.
printer friendly version