Chilling and Freezing: Are Temps on Spec in Your Freezer and Cold Room?

Originally published in FOOD Engineering Magazine - Chilling/Freezing

Original Article  |  Product website: Wireless Temperature Sensor | Yokogawa America

Chilling and Freezing: Are Temps on Spec in Your Freezer and Cold Room?

by Wayne Labs

Recently, I attended a webinar put on by our sister publication, Food Safety Magazine. During the discussion, I was surprised to hear that many food companies are still relying on the old-fashioned clipboard and paper charts to record key temperatures in chillers and freezers. Unfortunately, data often gets buried in binders, and there's no quick and easy way to generate insights on temperature shifts.

With manual data recording, key temperatures may get missed entirely ( either by distracted or new employees), and illegible scribbles won't get accurately transferred to an automated system, if it indeed exists. The lack of real-time critical temperature information in the plant or warehouse shouldn't, however, be an issue today because wireless temperature transmitters are affordable and can be placed in key remote locations - where a person may forget to check. 

Why rely on humans to take temperature readings in chillers and freezers when networked wireless devices can "make the rounds" more efficiently and accurately? While FE has covered chillers, freezers and their related systems and refrigerants in previous articles, based on the webinar discussion, a look into the automated recording of temperatures in cold storage rooms seems worthwhile. [1, 2] Certainly, newly-built cold storage warehouses and manufacturing structures have sophisticated wired and wireless systems for flexible and automated zoned temperature control. Older facilities - not so much. 

Automated Data Collection of Temperature Exceeds FDA Regulations

FDA’s regulations (21 CFR Part 117.93) don’t specify specific warehousing and distribution chiller and freezer temperatures — they’re performance based. It puts the onus on the operators to determine safe storage temperatures and maintain them. However, in referring to FDA’ s Food Code 2022 (Chapter 3), a good benchmark is to use 41°F (5°C) for T/TCS (Time/Temperature Control for Safety) for refrigerated foods. For frozen food, which is to be “maintained frozen,” typically 0°F or −18°C is appropriate. Specifically, the Food Guide says, “A food that is labeled frozen and shipped frozen by a food processing plant shall be received frozen.” There is a different requirement for raw eggs, which says that “Raw eggs shall be received in refrigerated equipment that maintains an ambient air temperature of 7°C (45°F) or less.”

How often should temperatures be checked? For storage-only facilities (warehouses holding unexposed packaged refrigerated foods that require T/TCS), FDA requires operators to:

“Monitor the temperature controls with adequate frequency” to assure they’re consistently performed (you set the frequency based on risk). (Legal Information Institute (21 CFR 117.206))

Review monitoring & corrective-action records within seven working days (or justify a longer timeframe in writing). (Legal Information Institute (21 CFR 117.206))

For processors, preventive-controls verification requires calibration/accuracy checks and timely record review, but still leaves monitoring frequency to the operator’s hazard analysis/plan. (See 21 CFR 117.165 - Legal Information Institute.)

Part 117 doesn’t specify a numeric tolerance for temperature sensors used in chillers and freezers. However, it does require calibrating monitoring/verification instruments or checking them for accuracy per the operator’s written procedures. As a reference, the FDA Food Code specifies thermometer accuracy of ±2°F (±1°C) for food probes and ±3°F (±1.5°C) for ambient air/water devices — commonly adopted in industry QA specs, though not binding on processors under Part 117. [3]

Automation is allowed but not required. For warehouses, FDA explicitly allows either affirmative records (e.g., routine manual/automated logs) or exception records (typical of continuous automated systems that only log/alert on deviations). Part 117’s verification framework supports either approach, as long as the operator monitors at an adequate frequency, calibrates/checks accuracy, takes corrective actions and reviews records.

Why Automate Temperature Readings in Cold Storage?

If you’re not depending on a person to make designated temperature readings in cold storage (chillers and frozen food) areas, then you may have a wired system of temperature sensors in place, which when using an automated data collection system will be more reliable than any manual system.

However, the location of the wired sensors established 10 or 20 years ago may not meet your specific product application(s) today, especially if you make several different products requiring different chill-down timings or final temperature. It may not be easy to move the wiring to accommodate a sensor location change — and some of the sensors may be inoperative anyway due to broken wires and/or damage from forklifts or their cargo. Considering the inflexibility of wired systems and effort required in manual recording, wireless temperature and/or humidity sensors make sense for many reasons.

Wireless temperature sensors/transmitters make it easier to monitor product cool-downs in different areas of the freezer or chiller. With the ability of a wireless temperature transmitter to allow both an internal (ambient sensor) to check the overall unit (freezer/chiller) temperature plus accept a wired sensor input, an operator can monitor an internal (case, carton or product) temperature to verify the T/TCS cool-down rate — even while checking various areas in the cooler. Being able to move ambient temperature sensors freely around the space lets operators check for temperature gradients in the cooler — or section off spaces with temperatures that better match certain products.

Wireless sensors substantially reduce the cost of temperature monitoring in highly regulated environments such as food processing and cold storage, says Ray Almgren, CEO of Swift Sensors. “Many of our largest clients are claiming a ten-fold reduction in annual costs by moving from their legacy wired systems to our modern wireless cloud-based monitoring system.” Swift Sensors offers several types of wireless temperature and humidity sensors that can measure −100°C to +300°C and 5% to 95% RH.

Most process control vendors offer wireless temperature transmitters that fit into wireless networks. According to Adam Edison, global product manager, Emerson’s Rosemount Synchros temperature monitor can measure ambient/environmental temperatures from −40 to 185 ºF. Additionally, when needed, this device can be mounted to assets/equipment and monitor surface temperatures from −40 to 230 ºF. Maybe you want to keep track of an evaporator fan’s motor in your chiller or freezer space, so you know if it’s overheating. 

 

“The Sushi XS550 Wireless LoRaWAN temperature sensor operates reliably in environments ranging from −40°F to 185°F and is suitable for use in the refrigerated spaces and freezers commonly found in food processing plants and warehouses,” says R. Steven Webster, CD, P.L.(Eng), P.Tech(Eng), Yokogawa emerging solutions product manager/engineer. The XS550 features two thermocouple (TC) inputs and functions within ambient humidity levels of 0 to 100% RH (non-condensing).

Battery Life — Not to Worry

Years back, wireless sensor battery life may have been a concern, but today you will probably move sensors around to satisfy monitoring requirements before replacing batteries. “In a well-designed WirelessHART network, the Rosemount Synchros temperature monitor has the capability to maintain a one-minute update rate with a 10-year power module life,” says Ryan Lindsey, Emerson global product manager. In colder environments down to −40 ºF (−40°C), the battery life at a one-minute update rate would be reduced to seven years.

And the one-minute update rate is far better than what a human could accomplish in making the rounds. Almgren notes that operators can expect six to eight years of battery life, and when operating at −40°C, a slight degradation in battery life may be observed. Extending the reporting time to once an hour — still better than once or twice a shift that a human would do — you could expect up to 10 years.

Under optimal conditions — where the Sushi XS550 Wireless LoRaWAN temperature sensor maintains a robust signal strength (RSSI of -110 dBm or better) and operates within specified ambient temperatures — battery life is highly efficient, says Yokogawa’s Webster. At −40°F, with a reporting interval of once every hour, the expected battery life is up to 10 years for one or two temperature sensors. If the reporting interval is increased to every 10 minutes, battery life is approximately nine years with one sensor, and seven years with two sensors. Operating in extremely low temperatures (such as −40°F) may reduce battery performance compared to warmer environments, but the XS550 is engineered to provide multi-year battery life even under these demanding conditions.

Wireless Range — Cheaper than Copper Wiring

You can extend the range of your temperature sensing network through the use of wired gateways that receive data from wireless sensors or through wireless mesh networks — much like the power company uses the wireless meter on your house to connect to another — and another, until the data reaches a direct connection to the power company’s gateway.

For Swift Sensors, the maximum sensors-to-gateway distance is 300 ft. line of sight and 150 ft. non line of sight, Almgren says. Concrete walls and metal enclosures will reduce the wireless communication distance. Additional gateways can be added in a facility with wireless interference to ensure all sensors are monitored. The sensors automatically connect to the closest gateway.

The Rosemount Synchros temperature monitor includes native support for the a WirelessHART communication protocol, Edison says. WirelessHART networks are self-organizing and self-healing 2.4 GHz ISM-band (Industrial, Scientific and Medical) networks that manage multiple communication paths for any given device. If an obstruction is introduced into the network, then data will continue to flow because the devices have other established paths through the mesh network. Each device can communicate up to 590 ft. to another device within the mesh network. The range can be increased and obstructions to the signal can be alleviated by using repeaters and/or other measurement devices within the network.

Yokogawa’s LoRaWAN wireless solution operates with point-to-point networking rather than mesh networking, says Webster. However, since LoRaWAN utilizes the 900 MHz radio frequency, it is generally effective at penetrating walls and structures found in most applications. In warehouses or coolers with internal wall divisions, careful placement of gateways and antennas helps maintain reliable signal quality. If even more robust coverage is needed, deploying additional gateways or antennas is recommended to ensure consistent communication despite structural obstacles or potential sources of radio interference.

Wireless Network Options

While some manufacturers’ wireless sensor systems grew out of highly secure, must-get-through reliability of industrial wireless networks, suppliers are expanding capabilities and systems. While Lindsey notes that Emerson’s Synchros sensors use WirelessHART’s mesh technology, new network functionality is in sight. “In the future, Synchros products will also operate on cellular and LoRaWAN networks. Emerson’s service organization is equipped to support both network (architecture/topology) and device (provisioning/commissioning). Additionally, Emerson offers a suite of online tools to help users along their wireless journey.”

“Our wireless sensors use the Bluetooth Low Energy (BLE5) standard protocol to communicate with our IoT gateway,” says Swift’s Almgren. “The gateway then communicates over the internet via ethernet, Wi-Fi, or cellular. Our solutions are designed to be self-installed. Very little technical knowledge is required.” For those users needing extra assistance, Swift Sensors has regional installation partners to help out.

Yokogawa’s Sushi sensors connect via the LoRaWAN protocol to its gateway, which in turn, can connect to standard Wi-Fi, public service bands or cellular networks to output collected sensor data. Yokogawa also provides support to users needing assistance in configuring systems.

Calibration Mostly Out of Users’ Hands

Depending on the sensor, calibration is slowly becoming less of a task or no task at all for users, greatly simplifying operation and reducing lifecycle costs. “All of our temperature sensors can be calibrated in the factory, at an ISO 17025 calibration lab, or on-site at the customer’s facility — all according to NIST standards,” Almgren says. “The Swift Sensors Console includes a feature we call the ‘Calibration Workbench,’ which streamlines and simplifies the calibration process. Calibration frequency is set by the customer or the regulatory standard they follow. Annual calibration is the most common frequency we see.”

More expensive industrial sensors may pay for themselves. Why? How about temperature sensors requiring no initial calibration, or literally, no calibration at all? Yokogawa XS550 Sushi temperature sensors are designed to operate without the need for initial calibration or ongoing recalibration. All accuracy specifications are detailed in the company’s “General Specifications,” according to the specific thermocouple type used. Edison says there is no calibration required for the lifespan of the Emerson Synchros sensors.

Wireless Sensor Range/Distance Considerations

According to Yokogawa’s Webster, the maximum point-to-point range between the Sushi wireless sensor and its associated gateway — both operating at 900 MHz — depends on the installation environment:

• Clear Line of Sight: In open environments with unobstructed visibility (such as open fields, along rivers, or on offshore platforms), the typical communication distance can reach up to approximately four miles or greater. *

• Partial Obstructions (Outdoor/Industrial): In outdoor areas where direct line of sight cannot be fully maintained — such as tank farms or facilities with dense piping — the expected range is around 0.6 miles.

• Indoor or Heavily Structured Environments: For sensors installed indoors or in areas surrounded by structures, like within production facilities or heavily shielded enclosures, the effective range depends greatly on the specific installation and the placement of both sensors and gateways. To enhance connectivity in such environments, antennas can be installed at elevated locations, or multiple gateways/antennas can be deployed within the facility.

*Ed. Note: According to the radio path loss formula, with all things being equal (antenna gain, transmit power, receiver sensitivity), radios (i.e., wireless sensors) operating at 900 MHz (compared to devices operating at 2.4 GHz) will see an 8.5 dB signal improvement, relating to a coverage at 900 MHz roughly 2.7 times the distance possible at 2.4 GHz for an unobstructed outdoor terrain.

Data Logging Options Abound

With today’s digital systems, you just expect data logging — and you get it. Lindsey describes Emerson’s approach now and into the future: Synchros devices integrate into WirelessHART gateways that interface with existing host systems via a wired Ethernet connection using industrial standard protocols, including OPC, Modbus TCP/IP, Modbus RTU, and Ethernet/IP. An example of a host system is Emerson’s MES software, such as DeltaV. In the future, cellular products will offer cloud storage functionality.

“Our Console is cloud-based and can be accessed from any desktop or mobile device,” Almgren says. The Console displays analytics in real-time, sends event alerts and creates comprehensive reports. Data can be exported as a CSV or PDF file. And our platform can be seamlessly integrated into existing applications using our secure API.

Yokogawa offers a variety of data logging solutions for the Sushi wireless sensors, including both on-premise and cloud-based options, Webster says. For on-premise data logging, solutions such as GA10 Data Logging Software and CI Server Software are available. For cloud-based needs, Yokogawa provides a Wide Area Monitoring Solution (WAMS) and OpreX Asset Health Insights (AHI). These platforms can integrate with HMIs, food safety management systems, MES software and other industrial applications, providing flexible options for local or remote data storage and analysis.

 

References:

[1] “Tech Update: Freezing & Cooling,” FE, Nov. 23, 2022

[2] “Upgrade Chilling Equipment to Industrial Heat Pumps,” FE, October 10, 2024

[3] FDA Food Code 2022, Version 2023; FDA Website download (8 JAN 2025)