Tektronix Encore

Calibration Baths Fine Tune Temperature

June 06, 2024

Temperature is a significant variable for many electronic devices and must be monitored, but it must be done accurately. To serve that purpose, temperature calibration baths provide a dependable means of calibrating temperature sensors of different shapes and sizes, often many at one time. Temperature sensors are used in many markets, including aerospace and defense (A&D), automotive, environmental monitoring, healthcare, and testing. Calibration baths themselves come in many shapes and sizes and selecting the optimum bath requires a basic understanding of how a temperature calibration bath works and how its specifications can be used to compare different models. Whether hot, cold, or across wide temperature ranges, an application, and its unit under test (UUT) will establish the required parameter limits for a temperature calibration bath, such as the bath volume, the type of fluid in the bath, and the adjustable temperature range.


Often simply called calibration baths, temperature calibration baths are not just tanks for temperature-controlled fluids. They are integrated systems consisting of a stainless-steel tank, a condensing coil and cooling plate, a heater, propeller, and stirring motor. These components combine to maintain selected fluids within the tank at tightly controlled temperatures across a wide temperature range. By immersing temperature probes and other UUTs in the fluid at a single temperature or any number of temperatures within the calibration bath’s temperature range, the probes and UUTs can be calibrated and tested at precisely known and stable temperatures.


When evaluating temperature calibration baths, parameters for comparison include the volume, size, and weight of the bath, its total temperature range, power consumption, heating and cooling times, and stability and uniformity of a set temperature. In use, calibration baths are usually set to one temperature at which they calibrate probes or UUTs. With a temperature-controlled fluid, they are better than a dry well when calibrating multiple probes, even when the probes differ in size or type. Probe clamps can be used to safely hold probes or UUTs in place during a temperature calibration, without impacting the accuracy of the calibration. The number of probes or UUTs being calibrated at one time will affect the temperature stabilization time of a calibration bath when changing temperatures, with more time needed to stabilize the temperature of the calibration bath when more probes are being tested at the same time. Temperature calibration baths are capable of wide temperature ranges, with the best calibration results usually achieved when starting at the highest temperatures and progressing to the lowest temperatures.


Consider Calibration Needs

A company synonymous with temperature calibration baths (and many other calibration units, such as pressure calibrators) is Fluke Calibration. The Fluke 7340 is a compact benchtop temperature calibration bath capable of setting precise, stable temperatures over a range of -40°C to +150°C. It handles 2.4 gallons of bath fluid but measures only 12.0 × 24.5 × 23.0 in. (305 × 622 × 584 mm) and weighs 78 lbs. (35.4 kg) for ease of repositioning and placement. Standard units run on 115 VAC, 60 Hz, and 15 A while model 7340 calibration baths are also available with an option for 230 VAC, 50 Hz, and 8 A.


The model 7340 temperature calibration bath features an easy-to-read, eight-digit, light-emitting-diode (LED) display and can show temperature in degrees Fahrenheit (F) or Centigrade (C). It has automatic refrigeration control and an RS-232 digital interface for computer/software connections, with optional General-Purpose Interface Bus (GPIB) port available.


What makes its compact size and ease of use so appealing is outstanding performance, which it provides with a variety of fluids, including water, ethylene-glycol/water (commonly known as automotive antifreeze), mineral oil, and silicone oil. The choice of liquid depends on the desired temperature range for the calibration bath. For example, water has a temperature range of 0°C (below which it freezes) to about +95°C while a 50%/50% mix of water and ethylene glycol and its higher viscosity has a temperature range of -35°C to +110°C.


Powered by a 700-W heater, this benchtop temperature calibration bath has a heating time of 60 minutes when raising fluid temperature from +25°C to +150°C with 5012 oil. It has a cooling time of 110 minutes from +25°C to -40°C when evaluated with the ethylene-glycol/water mix. Temperature can be set with 0.01° resolution and 15 to 20 minutes time is required for the temperature to stabilize after a temperature change. Following that stabilization time, the temperature barely fluctuates, with stability of ±0.005°C at -40°C and ±0.005°C at +25°C for ethylene glycol and ±0.007°C at +150°C for 5012 oil. The uniformity or consistency of temperature throughout the liquid volume is similarly excellent: ±0.006°C at -40°C with ethylene glycol, ±0.005°C at -40°C with water, and ±0.010°C at +150°C with 5012 oil. In addition to its precision, the 7340 is a ruggedly built machine, with 304 stainless steel used for all parts immersed in fluids. Because of the extremely elevated temperatures, users should exercise caution when using these units, and remember that fluids expand when heated and not overfill the tank.


For users in need of greater portability, there are much smaller temperature calibration baths, such as the Fluke 7102 and Fluke 7103 micro-baths, at a fraction of the size and weight of the model 7340. Model 7102, for example, provides a temperature range of -5 to +125°C with accuracy of ±0.25°C and settable resolution of 0.01°C or F. Measuring just 7.2 × 12.0 × 9.5 in. (18 × 31 × 24 cm) and weighing only 15 lb. (6.8 kg with fluid), it has fluid capacity of 0.75 L (1.6 pints). It can heat from +25°C to +100°C in 30 minutes and cool from +25°C to 0°C in 30 minutes. It features stability of ±0.015°C at -5°C and ±0.03°C at +121°C, both measured with oil, and uniformity of ±0.02°C across the fluid volume. Model 7102 draws 1.8 A from a 115-VAC power source and is available for use with 230-VAC supplies (0.9 A) as an option.


With a wider temperature range in a slightly larger package, the Fluke model 7103 covers -30 to +125°C with accuracy of ±0.25°C and resolution of 0.01°C or F. Measuring just 9.0 × 13.2 × 10.5 in. (23 × 34 × 26 cm) and weighing only 22 lb. (9.8 kg with fluid), it has fluid capacity of 1.0 L (2.11 pints). It can heat from +25°C to +100°C in 35 minutes and cool from +25°C to -25°C in 45 minutes. It features stability of ±0.03°C at -25°C and ±0.05°C at +125°C, both measured with oil, and uniformity of ±0.02°C.


These are just a few of the temperature calibration baths available for rent from Transcat | Axiom Rental Equipment, most equipped with RS-232 ports for connection to a computer and test software. The Fluke 6330, for example, at 12 in. wide and 19 in. high, is ideal for benchtop use. It can maintain bath temperatures as high as +300°C (+572°F) with stability of ±0.015°C and uniformity of ±0.020°C.

For more information on model 6330 and several additional Fluke temperature calibration baths, including the Fluke 6102 and Fluke 6331, please visit our website or contact us for guidance at (760) 806-6600.

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