Jofra Dry-Block Temperature Calibrators Offer Excellent Solution For Calibrating Difficult Sanitary Device

ALBANY, New York - Accurate and reliable temperature measurement is especially critical in the food and beverage processing, where it is frequently part of a facility’s Hazard Analysis and Critical Control Point program. Verification of temperature sensor accuracy is often needed to ensure maintenance of optimum temperatures for health, safety, food quality and energy efficiency. Unfortunately, the accurate calibration of sanitary temperature sensors presents unique challenges.

The wide diameters, short lengths, and large flanges of most sanitary temperature sensors work together to reduce the overall accuracy of calibrations performed using common single-zone dry-block calibrators. As these calibrators only control the temperature deep within their blocks, short sensors may not reach into the regulated temperature zone.

Additionally, the large heat-dissipating sanitary connection flange further aggravates the temperature deviation at a short sensor by increasing the temperature gradients across the dry block. Lastly, the large connection flange and head make it difficult, or impossible, to insert a reference temperature sensor next to the sanitary sensor.

The innovative design of the JOFRA ATC-156B dry-block temperature calibrator with its specialized Sanitary Sensor Calibration Kit from AMETEK Test & Calibration Instruments overcomes each of these challenges. The resulting calibration system makes performing and verifying sanitary and short sensor calibrations fast, easy and extremely accurate.

The specialized sanitary sensor kit includes custom inserts with flanges that correspond to the flange on a sanitary sensor as well as a specialized reference temperature probe. When the flange surface of the sensor contacts that of the insert, the temperature gradient due to heat dissipation is greatly reduced while the sensor is provided with stable physical support.

To minimize the remaining temperature gradient throughout the dry block, the ATC-156B features a unique dual-zone heat control system that incorporates independent energy sources at the top and the bottom of the block. The energy sources are controlled in such a way that the temperature is kept uniform throughout the block. The block’s upper section automatically compensates for heat dissipation that occurs through the sensor under test as well as to atmosphere thereby significantly increasing the temperature accuracy of short sensor calibrations.

The final accuracy-improving feature of the system is a specialized JOFRA STS102 reference probe that is specifically designed to be positioned in parallel with the sanitary sensor during calibration. When used, this special sensor enables a calibration accuracy of ±0.04°C. The resulting ATC-156B temperature calibration system offers a complete, portable calibration solution for the food and beverage industry.


Dry-Block Calibration



Dry block calibration, which accounts for about 95% of all industrial temperature calibration applications, is very simple in principle. A metal block is heated and cooled to a specific temperature that can be set very precisely. The sensor under test is placed in a hole in the heating block, in close contact with the block so that it reaches the same temperature. This has a number of benefits versus liquid-bath calibration.

A dry block can be heated and cooled much more quickly, and an individual calibrator can cover a much greater temperature range. In addition, there are no dangerous liquids involved, and the instruments are typically smaller, lighter and more portable, making them easier to move from location to location for calibration.

Single-zone dry-block calibrators use a single heating element that runs the entire length of the block. These calibrators offer reasonable accuracy and stability, but there is a risk of heat loss from the top of the calibrator where the sensor emerges, leading to a temperature gradient down the block.

Greater temperature homogeneity can be achieved using dual-zone heating technology, in which there is an extra heating zone at the top of the block to compensate for heat loss. Control of the upper zone heating can be carried out by continually measuring the difference in temperature between the top and bottom so that the energy distribution between the two zones is determined according to the actual thermal load of the sensor under test.

This active dual-zone heating approach is employed on the entire range of JOFRA ATC calibrators from AMETEK Calibration Instruments. This design provides equivalent performance as a liquid temperature bath and eliminates the need for insulation of the sensors under test. It also is possible to calibrate liquid-filled and other mechanical sensors, as well as RTDs, thermocouples, thermistors, short sensors and sanitary sensors, and importantly, test several sensors simultaneously.

The JOFRA ATC series are “standalone” units that can be used to perform completely automatic calibration routines but may also be connected to a computer for uploading of results or remote control of calibration routines. The use of this technique can significantly reduce calibration times.


Temperature Calibration for Hygienic Applications



In general, the temperature for cleaning processes is 90oC, although different cleaning fluids may be used according to application. Temperature sensor accuracy requires a difference of less than -0.5C. Temperatures required for pasteurization processes are generally between 70oC and 80oC, depending on flow. However, the accuracy of the temperature sensor must have a difference of less than -0.3C.

The JOFRA ATC-156B dry-block calibrator more than meets these requirements. Temperature stability of the calibrator is + 0.01oC and is guaranteed for a full twelve-month period. A calibration accuracy of ±0.04°C is achieved when the JOFRA STS102 probe, included in the sanitary sensor kit, is placed in parallel with the sanitary sensor under calibration. In addition, JOFRACAL software is available to control the entire complete calibration procedure. The software can be downloaded at www.jofra.com.

With JOFRACAL, results can be stored and hard-copy certificates produced to provide a calibration audit trail. All calibration and historical data are stored for each sensor to monitor drift and optimize recalibration intervals. The software also provides a comparison between the process readout value and the reference value--a measurement that is typically required within HACCP systems.

With this method, all the sensors in the process are calibrated to a set pattern. They are calibrated at several different points at a range of pre-programmed temperatures within permitted tolerance levels. Each calibration takes between 45 minutes and one hour compared with four hours using a liquid bath calibrator. Just as important, this method has the added benefit of allowing an engineer to carry out other tasks while calibration is in progress.

JOFRA dry-block calibrators are part of a comprehensive line of pressure, temperature, signal, texture analysis and force-measurement products marketed by AMETEK under the JOFRA, LLOYD, and MANSFIELD & GREEN brand names. AMETEK T&CI-Americas is a unit of AMETEK, Inc., a leading global manufacturer of electronic instruments and electromechanical devices with 2006 sales of more than $1.8 billion. For more information, contact AMETEK T&CI -Americas, 7A Harriman Campus Road, Suite 310, Albany, NY 12206. Phone: 518-689-0222. Fax: 518-689-0225. Web site: www.ametektcia.com