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Dynamic Load Compensation for Dry Block Temperature Calibration


JOFRA is continuously seeking new ways of improving temperature calibration. The DLC calibration correction technology is yet another state of the art innovation within temperature calibration. DLC is short for Dynamic Load Compensation: the principle is innovative and patent pending.

What is the Dynamic Load Compensation system?

The Dynamic Load Compensation system combines a measuring/control system with a newly developed Dynamic Load sensor.

What is the purpose of the Dynamic Load Compensation?

The DLC system has been developed to deal with a major contributor to calibration errors. A dry-block used as a calibration instrument has some inherent error mechanisms. It is a fact that the sensor under test will affect the calibration accuracy during calibration. The sensor transmits energy to and from the calibrator. This heat exchange between the calibrator and the environment has a considerable negative impact on the calibration accuracy. The extent of the error depends on many factors: sensor size (diameter and length), number of sensors in the well and the difference between calibration temperature and ambient temperature.
In other words, calibration accuracy is actually influenced by the actual load of the calibrator.

How does the DLC system work?

JOFRA temperature calibrators are already famous for their active dual-zone calibration principle.
With the DLC system, we have taken this well-proven and acknowledged dual-zone principle one step further. The load compensation is now active both within the heating block and inside the insert during calibration.
The DLC sensor measures the actual temperature difference between two defined points inside the insert. See the purple dots. The DLC sensor is designed to process input to the heat control system of the calibrator to ensure that the axial gradient deviations in the lower 60 mm of the insert are kept to a minimum. The temperature difference between the bottom and the zone at 60 mm from the bottom is controlled within a few hundreds of a degree.
The DLC system reacts immediately to changes in the load of the insert and controls the heat distribution to achieve the minimum axial gradient.

How much does the DLC system improve your calibration results?

The DLC system improves the calibration accuracy significantly. This may be illustrated and proven by two different test scenarios.
The first scenario shows the improvements when measuring in the insert. The graph below illustrates the temperature change in the insert as a function of the distance from the bottom. Ideally this should be a straight line with no temperature variation vertically in the insert. If so, the axial gradient would be zero. However, this is not the case in practice.
To prove that the DLC functionality will improve the axial gradient, three tests have been performed.
The first test is to put a very light load on the RTC calibrator, which should produce a very little axial gradient (blue line). The load is a 4 mm external reference sensor, a 3 mm sensor and the DLC sensor. The maximum deviation from the ideal straight line is 0.015°C.
The next test is to load the RTC calibrator more heavily (red line). A thicker, 10 mm, sensor is added to the configuration detailed in the previous test. The DLC functionallity is not activated. The heavier loading of the calibrator causes a nonlinear axial gradient. The maximum deviation from the ideal straight line is 0.160°C.
The last test is carried out with exactly the same load as above, but we will now activate the DLC functionallity to see how efficiently the DLC will straighten the gradient (green line). The maximum deviation from the ideal straight line is 0.025°C.


What are the advantages of the patent pending DLC system?

  • Calibration of several sensors simultaneously
  • Calibration of large diameter sensors
  • Since no standard temperature sensors have a thermo sensitive lenght beyond 60 mm, it is no longer necessary to know the length of the thermo-sensitive part of the sensor. Just plug it in!
  • The DLC indicator shows that the dual-zone is active and working
  • A perfectly working calibrator. The DLC value is very close to 0.00 when the calibrator is loaded or not loaded
  • Calibration value indication. The DLC indicator shows when the temperature homogeneity in the lower 60 mm part is achieved

What are the important benefits for the user?

• Saves time by calibrating more sensors simultaneously

• Calibrating big diameter sensors without loosing accuracy due to heat conduction

• TSL (Thermo Sensitive Length) independency. Safe, secure and accurate calibration results without spending time to get sensor specifications from your supplier

• The DLC function minimizes the influence from sensor production tolerances like the Pt100 element being mounted in various positions in the sensor

• All temperature sensors that can be placed in the bottom of the calibrator will be calibrated without error

• The displayed DLC value indicates when the optimum temperature homogeneity is achieved

• The displayed DLC value shows when the load has no influence on the calibration result

• When the DLC value is close to zero, the calibration technician knows that the calibration results are reliable

• The DLC indicator proves that the dual-zone is active and well-functioning

• The DLC in conjunction with the stability indicaton show when the calibration value is ready. The green-zero rule


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