No one forces you to measure flow, level or pressure in your process (unless maybe your process uses HPP for sterilization). 

Sure, these measurements are important—along with a host of other process variables you could instrument. But temperature is that one measurement that’s dictated by governmental regulations to prove that you have a kill step in your process. Beyond that, there are rules for keeping fresh food under a certain temperature to keep it safe both in transit and storage, and—just as important—maintain its quality so you don’t have to throw it out prematurely. 

Three years ago, we looked at automated temperature monitoring and control and sensor technology in some detail, but in this article, we’ll delve more deeply into the networking aspects of temperature measurement plus monitoring product temperatures in storage. 

Let’s start with a simple overview, beginning with the sensor itself. In the food and beverage industry, the types of temperature sensing devices used vary by application, but the primary types are thermocouples (T/Cs) and resistance temperature detectors (RTDs), says Ryan Beesley, CAP, regional engineering manager for Concept Systems Inc., a Control System Integrators Association (CSIA) certified member. Generally, T/Cs are used in low-cost applications that require fast response and lower accuracy than RTDs. They are best suited for high temperature applications. RTDs are typically used in applications below 120°C and are the most stable and accurate at moderate temperatures.

“The most common items we have provided for food processing are FDA and USDA reference thermometers,” says Alan Clark, Palmer Wahl Instruments application engineer. The only two thermometer types that will meet all the FDA and USDA regulations are mercury-in-glass and RTD thermometers. The machine control and recording devices that are installed to control the process must be in agreement with the reference thermometer(s). They must never be allowed to display or record a higher temperature than the reference thermometer is displaying, as it is the ultimate temperature standard, adds Clark. “We also can and have supplied the RTD sensors for the controller and/or recorder.” In fact, Clark says most applications in the U.S. have used RTDs with electronic recorders and data loggers.

From analog to digital

Without transmitting the sensor’s weak signal to a monitor, controller, chart recorder, data concentrator or other device, you’d might as well be using a thermometer and clipboard. Typically, analog 4-20mA transmitters are the standard means of getting temperature measurements to PLCs from T/Cs and RTDs, says Beesley. Highway Addressable Remote Transmitter (HART) protocol-enabled devices have become the go-to for industrial applications where accessibility and ease of programming are desired. These devices have allowed technicians to parameterize, monitor, and calibrate devices remotely using a HART communicator. 

More recently, instrumentation manufacturers have developed software applications that can be run from a PC, using a USB HART converter to accomplish this task. As a standard protocol, HART configuration software from many vendors is capable of programming nearly every type of HART device. Furthermore, PLC manufacturers have integrated HART communications into their analog I/O modules, allowing access to the devices through the PLC programming software, says Beesley.

In recent years, with the development of the ISA100 wireless network protocol, temperature monitoring devices have begun to transition into a wireless solution. ISA100 is becoming more and more popular as the preferred network protocol for industrial wireless communications, says Beesley. The ease of installation, improvements in network efficiency, reduced latency (< 100 ms), and security improvements have made ISA100 wireless devices invaluable for industrial applications where existing and new installations need flexibility and must be easy to configure.

Besides supporting Wireless HART, Endress+Hauser offers a full slate of hygienic, self-calibrating temperature assemblies for process monitoring with its iTHERM line, which includes Bluetooth communications for connecting with HMIs, says Robert Villarreal, product marketing manager—temperature and system products. In addition, Ethernet-ready digital recorders and data concentrators can be used for remote monitoring and diagnosis. For example, E+H’s Model RSG45 Memograph data manager can be used as a remote I/O concentrator, which reduces wiring back to a control system.

TEGAM also makes good use of Bluetooth technology, according to President Adam R. Fleder. “Our Bluetooth wireless thermometer enables connecting a temperature, place and time with much less effort than a clipboard.” The user routinely measures a critical process temperature and automatically stores the readings in a corporate database or quality management system with the touch of a single button. TEGAM’s open system can be seamlessly connected to a large corporate infrastructure by using a software development kit that provides examples and source code for custom applications. The company also supplies advanced temperature calibrators so that both heating and cooling equipment can be routinely and easily calibrated for consistent results.

On the road

Long known for its Rosemount industrial wired and wireless temperature transmitters, Emerson has a full suite of in-transit temperature monitoring solutions. “Our GO Real-Time trackers and loggers can be placed on truck, air, rail and intermodal containers to track perishable products in transit,” says Kevin Stultz, global product manager, Rosemount Temperature. These devices can automatically transmit their temperature and location data to Emerson’s Oversight cloud portal using cellular communications. These devices are simple to use and require minimal human interaction. Users can be notified in real time in the event of an issue, and all in-transit cold chain information is available in Oversight for ongoing supply chain reporting and analysis, says Stultz. 

Monnit specializes in turnkey wireless sensors, gateways (Ethernet-based and cellular [AT&T, Verizon, et al.]) and sensor management software, says Nick Mecham, vice president, business development. “Able to accompany food from farm to fork, our sensors support butchers, food processors, manufacturers and retailers. Beyond remote monitoring, our CFR21 part 11 compliant wireless temperature sensors provide automated data logging.” This function helps food processors and retailers become (and remain) compliant with the FDA’s FSMA. 

Within the past year, Monnit began offering wireless temperature sensors that carry a 25-month NIST (National Institute of Standards and Technology) accuracy certification. “Our certification laboratory went this route because of our sensors’ stability; after two years, they were finding that our sensors were still properly calibrated,” says Mecham. And given the breadth of its food production and service customers, this 25-month certificate is available on Monnit’s ALTA temperature sensor line, which spans from a compact coin cell-powered sensor to AA battery-powered and industrial-grade sensors.

Trends in temperature monitoring in the plant

Malisko Engineering, a CSIA certified member, provides automation solutions covering the full spectrum of the many process cells making up manufacturing; from raw ingredients through mixing, blending, reactions, thermal process, drying, agglomeration, pasteurization/sterilization, and finished product storage. In all cases, temperature monitoring and control is vital to the quality and integrity of the ingredients, intermediates and finished product.

Steve Malyszko, co-founder of Malisko Engineering, notes how modern process control has been applied to key industries. For example, raw ingredients, such as milk, are kept in jacketed silos where sensors monitor critical temperatures throughout with devices positioned at key locations, which then transmit their signals via an I/O system-connected to an Ethernet or wireless network to a process controller—such as a PLC or DCS—to manage chilled water to the jackets. Malyszko points out two areas that have seen significant change: the “interface” between temperature transmitters and the controllers/HMI/data historians and the “resident intelligence” built into the newer smart temperature transmitters.

I/O systems are critical in linking sensors to controllers. I/O modules accept signals from RTDs and T/Cs and relay these signals to the appropriate controllers. But these systems do more. 

“An I/O platform that offers a universal analog input module is an option to give you fast and accurate measurement of temperature signals,” says Rosh Chathoth Sreedharan, Rockwell Automation FLEX 5000 I/O product manager. “What’s more, these modules can also be configured at the individual channel level to work with mA current, voltage, RTD and thermocouple signals. This ability to use the same module for both temperature and other environmental measurements can help you realize hardware cost savings and a reduced design time.”

Another process needing tight control is baking, says Malyszko. Temperature sensors/transmitters tied to a process controller with a real-time data historian on premises or in the cloud provide control, typically embedded in zones within a continuously running oven tunnel. The baked products, such as cakes, pies or cookies, are heated and cooled to specific temperatures in each zone, which has a controller to determine how much heating should be applied.

Processors are going beyond monitoring in-process temperatures, says Concept Systems’ Beesley. They’re using advanced technology in monitoring raw materials (such as the milk example) for more efficient run scheduling. Temperature monitoring in process is used not only for quality assurance but also to ensure quality control further upstream. Using advanced model predictive control with temperature monitoring can increase production rates, decrease energy usage and improve product quality. At every point within the manufacturing process, temperature monitoring is giving operations the data that they need to make more informed decisions in real time.

However, having this data in a usable format for both OT and IT organizations still has a few obstacles, communications gaps or data silos, according to Josh Eastburn, director of technical marketing at Opto 22, a CSIA partner member. However, the good news is that there are solutions.

The desire to acquire more data for the organization and to overcome the obstacles to doing so is bringing technologies to the fore like industrial edge computing and IIoT-oriented communication protocols, says Eastburn. Edge computing builds on existing automation frameworks to bypass middleware—PLCs, industrial PCs, OPC servers, etc.—and improves local data processing and security. IIoT communication protocols, principally MQTT with Sparkplug B, build on this foundation to create new information architectures that allow many more data consumers to access data efficiently.

Rosemount 848T Wireless Temperature Transmitter
Rosemount 848T Wireless Temperature Transmitter provides high-density measurements via WirelessHART communications. This transmitter accepts up to four independently configurable inputs, reducing installation and operational costs per point through the use of a smart, reliable and secure wireless network.

With these abilities to communicate, today’s temperature sensors do more. For example, says Emerson’s Stultz, Rosemount temperature transmitters can provide redundancy and diagnostics, such as hot backup and sensor drift alerts, which allow for more uptime on critical processes and proactive warnings before failures occur.

Proactive means engineers actually can predict when a sensor will fail instead of reacting to a downright failure, according to Endress+Hauser’s Villarreal. Couple this ability with the speed of response and simplified calibration, and the result is precious time saved.

Being oriented at the cutting edge of IIoT, the trend that Opto 22 observes most commonly is the need to communicate critical process variables and key performance indicators to software systems and other parts of the organization. Moreover, predictive maintenance and business intelligence are two key applications driving this focus.

IIoT and remote monitoring via wireless sensors are not new to food manufacturing, says Monnit’s Mecham. However, data security is undoubtedly the next frontier because many IIoT device manufacturers have been betting on only using legacy IT security standards, which are proving to be inadequate for IIoT networks. And for manufacturers wishing to keep their secret sauce, well, secret, Monnit has confronted security head on by making data security the key ingredient of food production.

To shield temperature-related and process-related data, Monnit recently debuted SensorPrints software and the Advanced Edge Gateway to address end-to-end network security. The gateway provides sensor-to-server security by supporting MQTTS (MQTT + SSL) and device certificates. This Ethernet­-based gateway allows users to leverage Monnit’s array of wireless sensor types, gather IIoT data, and authenticate data via cryptographic validation (basically a sensor “fingerprint”). Validated data is then securely transmitted via MQTTS to a designated cloud provider or custom platform.

The trend is moving in the direction of integrating automated systems to monitor facility temperatures, ovens and blast chillers, says Eric Finnin, Texas Food Solutions director of food safety. Facility temperature monitoring is relatively cheap, so it can be adopted by plants of all sizes. The benefits of using such a system greatly outstrip its costs. However, if a system is cloud based, be sure to consider how the system connects to the cloud, what can be expected in long-term support, and whether backup is sufficient.

For more on integrating systems like spiral freezers with process control and building control/HVAC systems, see “No spiral freezer should be an island of automation,” by Ivy Arkfeld, mechanical engineer, VaCom Technologies

Trends in temperature monitoring in storage

Cold storage facilities employ many means of monitoring to ensure that the product is maintained at optimal conditions without compromising on energy consumption, says Beesley. Temperature sensors located in the refrigeration process ensure that the storage facility is being effectively climatized without over- or undercooling intake air. Sensors located throughout the facility monitor the ambient air temperatures, and in-floor RTD’s ensure that the foundation of the facility, where a large amount of energy is consumed, isn’t wasting energy.

Keep in mind that storage temperature will vary in different products, says Palmer Wahl’s Clark. This means different zones with different temperatures, atmospheres and pressures as well. For these storage areas, RTDs, T/Cs and in some cases thermistor temperature sensors will be used with or without transmitters. Most of the current thermometers being used have built-in data loggers or send a signal to a wearable, belt-mounted data logger via Bluetooth. (Depending on Bluetooth class of operation, its range is from less than 10 to 100 meters.)

TEGAM's Model 931B data-logging thermometer
With Bluetooth capabilities, TEGAM’s Model 931B is a single channel, digital data-logging thermometer compatible with type K, J, T, E, B, N, R and S T/C probes to provide a range of temperature measurements (-418 °F to 3308 °F) with a 1000 hour battery life using three AA batteries. Photo courtesy of TEGAM

TEGAM’s Bluetooth wireless thermometer can be set to collect data automatically on a programmable interval from 1 second to 24 hours, says Fleder. It will also compute the minimum, maximum, average and standard deviation of the readings to monitor the performance of any equipment for days, weeks or months.

But cold storage isn’t the only area where temperature related issues can occur. “Utilizing temperature [sensors] for bulk solids storage can increase fire safety by providing insight into hot spots or upsets for storage silos and vessels,” says Endress+Hauser’s Villarreal. Where temperature and several process variables need to be combined into one local device, a RSG35/45 Memograph advanced data manager can be used to transmit several sensors’ data over Ethernet.

“Automated data logging is no longer a trend, it’s an expectation that partners, i.e., distributors, wholesalers and retailers, have,” says Monnit’s Mecham. “They expect transparency throughout the chain of custody; this way, if food quality (or worse, safety) issues arise, investigations are streamlined.”

Historically, processors have not adopted wireless systems since their range and performance have been limited because of metal shelving and support structures. Mecham says his company’s ALTA wireless sensors are capable of working up to 1200 ft. (non-line-of-sight) with a “process friendly battery life.” In terms of temperature reporting, readings of up to one per minute are adequate for most environmental storage temperatures.

While temperature sensors themselves operate at their specified range in process media, keep in mind, whether in ambient cold locations or very warm spots, temperature transmitters and I/O equipment need to work in a wide environmental range—typically from -40° to +70°C, says Rockwell’s Sreedharan. 

For more information:

Concept Systems Inc.,
Emerson Automation Solutions,
Malisko Engineering,
Opto 22,
Palmer Wahl Instruments Inc.,
Rockwell Automation,
Texas Food Solutions,
VaCom Technologies,