Create a Customized On/Off Process Control Unit

In control theory, an on/off controller is a feedback controller that switches abruptly between two states. It is often used as a control method for a process which can tolerate ongoing change in the process value within a band, referred to as the hysteresis. A common example of an on/off temperature control operation is a residential thermostat. They control the temperature of your home, turning off the heating or cooling system at your comfort setting, waiting for some significant change to occur, then turning on again to eliminate that difference. The process cycles continually. Many process operations can utilize simple on/off control action to maintain suitable conditions.

Temperature Transmitter
Courtesy Smart Sensors

A PLC (programmable logic controller) can be a good candidate for creating your own on/off temperature controller with specialized additional functionality that suits your process. Implementing the temperature control operation is not difficult, and the use of a PLC allows the designer to integrate other useful functions into a single piece of hardware, functions that might not be available in a commercially available process controller.

The primary input device will be a transmitter with analog output compatible with the analog input on the PLC. For this discussion, let's assume this is a temperature control application that requires heating of the process. So, a temperature transmitter will be our primary input device. The primary output device will be a heater contactor or other power control device, the input of which must be compatible with the output of the PLC. Any other switches, pilot lights, alarms, or other devices will need to also be associated with a compatible PLC I/O point. 

The logic portion of the temperature control activity is not complex. The input signal from the temperature transmitter is converted to a working value. Depending upon the numeric muscle of your PLC, this value may be a floating point number, but integer values work suitably. Here are the logic steps needed.

• Read temperature input value
• Is temperature greater than or equal to the setpoint? If yes, turn off output for heater and proceed to the next step. If no, go to next step.
• Is temperature less than or equal to the value of setpoint minus a deadband value (more on deadband below)? If yes, turn on output for heater. If no, continue to other commands that provide your additional desired functions.

Here are some points to consider.

• Use a greater than or equal to, or less than or equal to comparison to assure that all possible numeric scenarios for process temperature are handled.
• Deadband is a value that you employ to keep your control output from chattering rapidly between the on and off state when the process value is very close to the setpoint. It can also be used, in this case, to slow down the on/off switching of the heater and reduce wear on a mechanical contactor. Keep in mind that a 16 or 32 bit number, which is what the PLC will use for internal processing of your temperature reading, may actually pass across the setpoint value rapidly, even though a digital display of temperature will appear to be relatively stable. The constantly changing values would cause rapid changes in the output if the comparison logic did not include a deadband value. The use of a deadband creates a range of process temperature where no change in the output occurs. 
• For this particular application, with its heating action, a separate limit control is advised. The device should derive its input signal from a source other than that of the PLC and the output of the limit control should provide a positive means of de-energizing the heater.
• Other functions easily programmed into the PLC include alarms, pilot lights to reflect heating activity, an on/off switch for the process, and other items limited only by your ingenuity.

Not every process needs PID control. This illustration focused on temperature, but the principles are the same for almost any process. A modestly powerful PLC can provide the processing power, and input devices for temperature, humidity, moisture, pH, liquid level, flow, pressure, and more are available. Share your challenges with a process measurement specialist and develop an effective customized solution for control of your process.

Intelligent Management for Process Sensors

Process analytical sensors can require scrupulous levels of attention and maintenance to continually deliver optimum performance. In some cases, overly frequent or involved maintenance is performed in order to avoid problems. Mettler Toledo, globally recognized leader in the development of process analytical sensors, developed a solution to streamline sensor maintenance and maximize reliability and performance.

The iSense software suite supports Mettler Toledo's line of intelligent sensors, monitoring and documenting sensor performance while maintaining real time indications of time to maintenance and calibration. Essentially, the iSense software provides guided sensor maintenance and continually verifies the operational health of the sensor to assure that delivered data is accurate and reliable.

There is much more to learn about how the iSense software and comprehensive offering of intelligent sensors can enhance process performance, as well as the efficiency of analytical operations. Reach out to a process analytics specialist with your analytical measurement challenges. Combining your process knowledge and experience with their product application expertise will yield an effective solution.

Improve Liquid Processing Performance With Sensor Technology

In the field of industrial processing, there is always a striving for improvement. Increasing output, improving output, and decreasing resource input are the watch phrases for process designers and operators in every industry.

Liquid processing often involves analytical instruments that produce periodic or continuous measurements of process conditions. The accuracy of these instruments will directly impact the quality and efficiency of the process, so great attention is paid to maintaining sensors and related instrumentation in top working order. Mettler Toledo, globally recognized leader in analytical sensor technology, provides a comprehensive solution for liquid analytical operations with its line of smart sensors and companion management software.

The ISM sensor technology couples the sensor with an onboard processor that continuously monitors sensor performance and delivers real time information about accuracy and time before maintenance. This empowers users to efficiently schedule maintenance tasks and operate with assurance that the data delivered by the sensor is reliable.

The video below sums up the ISM sensor benefits in under one minute. Share your process analytical challenges with application specialists and combine your process knowledge with their product application expertise to develop effective solutions.

Digital Sensor Technology For In-line Process Analytics

Digital sensor technology opens new
avenues for accuracy and efficiency
Courtesy Mettler Toledo

In-line process analytics deliver wide ranging data used to control production processes and assure the suitability and performance of end products. Strict adherence to established procedures and standards contribute to the accuracy and value of the measurements derived from instruments and equipment monitoring various process steps from start to completion.

Digital sensor technology, with an onboard microprocessor, provides a wealth of functionality not previously available that enhances accuracy and efficiency. Mettler Toledo is at the forefront of digital sensor technology for inline process analytics with their line of ISM (Intelligent Sensor Management) compatible sensors. The digital sensors interface with companion transmitters and software tools to deliver customers top flight process analytics performance.

• Simplified workflow.
• Increased measurement effectiveness and process confidence.
• Sensors are easily removed from the process for calibration, negating need for personnel to bring calibration gases or buffer solutions to the measurement point.
• Diagnostic functions provide easy to read tools, notifying operators of when and what to do to maintain proper performance.
• Each sensor stores its own set of calibration data, which is automatically uploaded to the companion transmitter.
• Self configuration executed when new sensor connected to transmitter.
• Supporting software facilitates the range of tasks necessary to maintain top flight operational status for every ISM sensor.
• Sensor output is a digital signal, not prone to degradation in the same manner as analog signals.
• Sensor learns from and adapts to process conditions to provide better overall performance.

There is much more to learn regarding how ISM sensors can dovetail into your process operation and deliver substantial increases in efficiency and accuracy. The document below provides the next layer of information. Reach out to an inline process measurement specialist, sharing your process measurement challenges. The combination of your process knowledge and their product application expertise will yield an effective solution.

Intelligent Sensor Management For Inline Process Analytics from Alliance Technical Sales, Inc.

New M300 Series Single and Multi-Variable Transmitters From Mettler Toledo

Mettler Toledo recently introduced a new line of transmitters to deliver maximum effectiveness from their array of water quality and process analytics sensors. The M300 is available in 1/2 DIN and 1/4 DIN sizes, with a single or dual channel configuration. Two versions are tailored for process analytics applications or water quality applications. Analog or digital ISM sensors for pH/ORP, conductivity, dissolved oxygen and ozone can be utilized with the new transmitter, which features intuitive operation and excellent ergonomics.

Learn more about the M300 transmitter and see it in action in the video. Reach out to a product specialist with your water and process analytical challenges, combining your process knowledge with their product application expertise to develop effective solutions.

New Dissolved Ozone Sensor

Mettler Toledo, under the Thornton brand, has released a dissolved ozone sensor employing the company's Intelligent Sensor Management technology that helps to streamline the use of sensors for measuring pH, conductivity, dissolved oxygen or ozone, and a host of other aspects of pure water. The pureO3 sensor technology provides rapid response in a sensor assembly with a built in digital measuring circuit and Intelligent Sensor Management (ISM®). The pureO3 is designed for monitoring low concentrations of dissolved ozone in semiconductor and pharmaceutical pure water samples, bottled water and similar applications. Minimal maintenance requirements and reliable long-term operation are hallmarks of this sensor.

How it works, in the company's own words...

"The pureO3 sensor uses a gas permeable membrane to separate the sample from the electrochemical cell inside. Ozone diffuses through the membrane in direct proportion to the partial pressure of ozone outside the sensor.The cathode and anode inside the sensor are polarized with a voltage to enable the electrochemical reaction of ozone. Ozone is reduced at the cathode while the anode is oxidized, producing a current in direct proportion to the amount of ozone present. The very low current developed by these sensors allows them to have a long life with low maintenance. An embedded temperature sensor enables temperature compensation to adjust for the changing permeability of
the membrane with temperature. In addition, the instrument uses the temperature value to convert the ozone partial pressure signal to a dissolved ozone concentration value by compensating for the changing solubility of ozone with temperature."

Benefits to the user from the ISM® based sensor.

• Full sensor identification by type and serial number.
• Calibration history with actual calibration, factory calibration, and last three calibration.
• Programmable timer to facilitate maintenance planning, reducing downtime.
• Starting calibration interval of 90 days.
• Time to maintenance function integrates ozone concentration over time, indicating replacement time for membrane body and electrolyte.
• Dynamic Lifetime Indicator for inner body used ozone concentration integration to predict life of inner body and membrane. Starting values, membrane body lifetime 180 days, inner body 1080 days.
• Sanitization counter allows the limit of ozone concentration and duration of sanitization cycleto be defined on the transmitter.

The pureO3 sensor with ISM operates with the M800 and M300 transmitters. ISM features enable users to maximize the lifetime of the sensors and minimize downtime by predicting when sensor maintenance is required. Contact a product application specialist for all the details. Share your process measurement challenges with experts, combining your process knowledge with their application expertise to develop the best solutions.

Technical Reference for Thermocouples and Reistance Temperature Detectors (RTD)

One of many industrial
temperature sensor
configurations
Smart Sensors, Inc.

Temperature measurement is probably employed in process control more than any other physical property measurement. Methodology for temperature measurement is well established, as is the industry providing instruments and devices for acquiring temperature data from almost any facet of any process. If you are even peripherally involved in process measurement and control, having a solid understanding of how thermocouples and RTDs work is a requisite to solving problems or servicing customers.

One manufacturer of a comprehensive line of thermocouple and RTD assemblies, Smart Sensors, Inc., produced a technical manual with all you need to know about temperature sensors for process measurement and control. The manual is included below for easy reference. It covers:

• Thermocouple theory
• RTD and thermocouple specification criteria
• Cable specifications for both sensor types
• Comparison of thermocouple and RTD attributes
• Thermowell and protection tube specification and selection
• Specifying temperature sensors for hazardous areas
• Reference data tables for both sensor types
• Practices for improving temperature measurement
• Calibration

The tech manual should be on the shelf or cloud drive of anyone involved in accomplishing, interpreting, or maintaining temperature measurement. The configuration options for temperature sensor assemblies are extensive. Reach out to a product application specialist and combine your process knowledge with their product application expertise to develop effective solutions to temperature measurement challenges.

Technical Reference for Thermocouples and Reistance Temperature Detectors (RTD) from Alliance Technical Sales, Inc.