Essential tips for Temperature Measurement in the Food Industry

Temperature control in the food industry is an essential input for a variety of reasons:

• Optimal food storage in freezers, fridges or near ambient control
• Cooking control for food processing
• Preservation process i.e. Pasteurisation
• Energy cost control
• Food hygiene through bacterial control
• Storage during distribution

Consistency is the secret in the recipe and the process used to make it. Surface contact and materials used in the design of the process effect flavour. Materials applied inside the process must be sanitary stainless, while outside the process, instruments and sensors are exposed to all types of grease, oil, fluids and even pests.

Using instrumentation and sensors that can endure these conditions and be applied with sealed sanitary connections and wells are critical for preventing contamination of your product in process.

Food manufacturers can save money in their process and increase profit on their final product by buying and installing instruments and sensors that:

• Reduce errors in processes which will result in less wasted product
  
  ==> Use .04% RTD sensors vs the standard .12% RTD sensor to reduce the amount of drift and therefore loss of accuracy whenever possible.
  
  ==> For surface mount applications where vessels cannot be penetrated ensure you are using sensors designed with flat tips for perpendicular mounting or magnet sensor holders to ensure best surface area contact
  
  ==> Smart instruments provide the ability to accurately monitor measurements, and you can trim input readings directly from sensors to achieve maximum relative accuracy, or match performance characteristics with your already-installed hardware.
  
  ==> Smart instruments with accurate and reliable sensors applied at the critical bottling or canning stage of your process can help ensure that your product is at the necessary temperature required to ensure high product quality and prevent spoilage after packaging.
  
  ==> You can use process indicators or instruments with display to provide visual reference of process status allowing you to act on observed changes quickly.

• Are highly reliable, reducing the need for service or replacement
  
  ==> Buying highly reliable instruments and sensors reduces cost by cutting replacement cost and reducing process interruption due to instrument and sensor failure.
  
  ==> Where there is constant vibration on machinery that runs 24/7, it is critical to use instrumentation and sensors that are rugged and reliable.
  
  ==> If agitation or vibration exists in your process, consider using sensors designed and built for processes with excessive vibration.

• Are easy to remove and reinstall without having to shut down your process, increasing your process throughput
  
  ==> Using thermowells or sanitary wells, you can remove sensors to calibrate or check temperature measurement repeatability to meet FDA requirements
  
  ==> Using flexible sensors, allows you to stock fewer sensor types, some are field cuttable cut-to-length that can fit in any thermowell or sanitary well.

Temperature Probes in the Food Industry

Temperature probes can be permanently fixed in vessels or pipelines or they can be hand held insertion probes with a local readout.

Temperature probes need to be designed to be food safe which means they are easily cleaned. In vessels, pressures are usually quite low so quick release flanges and fittings are frequently used.

Plant design for temperature probes need to allow adequate probe immersion to ensure the food product temperature is actually measured. Inadequate immersion may give a signal unduly influenced by the plant ambient temperature through conduction error.

Food industry temperatures are usually quite modest. Resistance Thermometers (e.g. Pt100) offer greater accuracy than thermocouples at lower temperatures. Resistance thermometers also avoid the complication of a thermocouple compensating cable requirement.

Permanently fixed probes often utilise transmitters, converting the temperature signal to 4-20mA for easy transmission around sites.

316SS is the normal stainless grade for food contact components, although the full assembly including connection heads can be 316 also.

Basic food safety requirements in the food industry mean that temperature sensors and systems should be frequently checked and calibrated.

To do this, temperature sensors need to be removed from applications and checked by comparison to known error standards, usually done at specialist calibration sub-contractors.

Systems can be checked using a calibrated sensor simulator. The known simulated signal can be input to the system and the site readout unit checked against the simulated signal. Sites often do this themselves.

Food sites often have temperature control issues in peripheral equipment that also needs to be addressed such as conveyor bearings and plastic bottle manufacture.

Why Use Non-Intrusive Temperature Measurement?

An assembly with a thermowell and temperature sensor is the most frequently used method of measuring a temperature internal to a process.

Thermowells allow for direct sensor immersion into a vessel or piping which helps provide an accurate measurement, however, the required process intrusion introduces complex design challenges and operational risks including leak points, process contamination and more.

Technology is available that provides accurate process temperature measurements using a thermal conductivity algorithm, eliminating the need for a thermowell or process penetration while significantly reducing installation time and costs.

Considerations when installing IT Temperature Sensors

Traditional contact thermometers are increasingly being replaced in the food industry by non-contact infrared temperature sensors (pyrometers), which offer an instantaneous response time, the ability to measure moving objects, and (because there is no need to touch the measured object) improved hygiene.

Accurate readings of food surface temperature can be obtained easily with general-purpose sensors, often with no configuration necessary. Low-cost sensors can be used for low temperatures and non-reflective nature of the food substances.

There are a few factors to consider when specifying and installing an IR temperature sensor:

• Ensure the sensor's measurement area is smaller than the object you are measuring. Ideally, the measured spot should be half the size of the target object, or smaller. Choose the sensor's optics and measurement distance to obtain the measured spot size you need. Most objects in the food industry are large enough to measure using a general-purpose sensor, some available with a choice of divergent or focused optics.
• For objects moving past the sensor, such as loaves of bread in a conveyor oven, or chocolate moulds, ensure the target object remains in the sensor's view for at least as long as the response time of the sensor.
• Some sensors can continuously output the temperature between objects on a conveyor and ignore the gaps between them. Look for configurable sensors with Peak and Valley Hold Processing. The hold period should be set via the sensor's configuration interface to match the time period between objects. The setting is then saved to the sensor's internal memory and applied to the analogue (voltage or current) output. Sensors with digital communications also have this capability.
• If the ambient temperature is high (such as near ovens and heaters), be sure to choose a sensor that can withstand it. Most sensors can be used up to 60-70°C, however thee are sensors available tat can withstand up to 120°C or 180°C ambient temperature.•Frozen food can also be measured using infrared sensors, which can measure temperatures as low as 40°C. If the ambient temperature is low, the optional air/water jacket can be used to keep the sensor heated above 0°C and prevent ice from forming on the lens.
• Stainless steel surfaces are best measured using a short-wavelength sensor.
• Steam can significantly affect the measurement, and is best avoided. Minimise the amount of steam by extraction, and continuously purge the sensor's lens with dry air, for the best chance of success.

Maintaining accurate temperature records

From initial ingredients processing through to delivery to the consumer, it is critical that temperatures are accurately maintained at specified levels and recorded for ongoing verification, to achieve this data loggers are the ideal solution.

Data loggers are small electronic devices which record environmental parameters over time, allowing conditions to be measured, documented, analysed and validated. They help ensure compliance with quality and HACCP controls; Food Standards Agency and EU QFF Regulations, and more.

Data loggers provide monitoring during processing, cooking, pasteurisation, cooling and freezing. They are used throughout the cold chain; in refrigerators and freezers; and during sterilisation procedures and in industrial dishwashers. They also help to verify if cooling equipment is working correctly.

They are set up to record at specified intervals and positioned as required, and have an alarm which activates if conditions fall outside a user-defined temperature range. Data from standalone units is downloaded via a USB cable to a PC for analysis.

For sites requiring remote data access or with multiple monitoring points (e.g. warehouses), radio and network enabled devices are ideal: data is collected automatically and accessed on a PC, on a LAN, or remotely over the internet.

BS EN 12830 compliant units are available to meet the demands of the frozen and chilled foods storage and transportation industries, and accompanying probes will monitor extremes of temperature. Loggers with an integral stainless steel stab probe are designed to monitor product core temperatures.

A wide choice of data loggers are available:

• Standalone, network enabled or wireless devices
• Multi-channel loggers to simultaneously monitor two parameters (e.g. temperature and RH) or multiple monitoring points using probes
• Rugged, waterproof and dustproof units
• Units with displays showing current readings as well as recording data
• Fully submersible, high temperature loggers
• Range of accompanying probes for measuring extremes of temperature or hard to reach areas

It’s all about the data!

The main purpose of temperature monitoring is to gain clear, concise and accurate data in order to verify conditions and/or make informed decisions about subsequent actions that need to be taken.

It is important that the recorded data is presented in a flexible and easy to understand format, and able to be exported for reporting purposes to other popular packages if required.

This article was contributed to by:

• Peak Sensors
• Calex
• Emerson Automation Solutions
• Moore Industries
• Gemini Data Loggers