Calibration

What is Dry Block Calibrator and how to use it?

What is a Dry Block Calibrator?

  • A dry block calibrator in other words is known as a dry well calibrator.
  • These dry block calibrators are used to calibrate various temperature sensors such as Thermocouples, Thermometers, Thermistors, and RTDs in a liquid-free enclosure.
  • Dry blocks are used when the sensors need to be tested for both accuracy and portability.
  • The dry block temperature calibrator consists of a portable metal insert with pre-drilled holes to insert sensors for measurement purposes.
  • There must be optimum thermal contact between the metal insert and the sensor for secure measurement of the temperature sensor.
  • Dry block calibrator used for testing and calibrating various temperature sensors such as Thermocouple, RTDs, or Thermometer.
  • Dry block calibrators’ functions well for calibrating RTD, Thermocouples, and Thermistor probes having straight and small diameter sensors.
  • A dry block calibrator is not considered for calibrating liquid-in-glass thermometers because they easily get stuck and these have a chance of breaking during the calibration.
  • But temperature baths are recommended for calibrating liquid-in-glass thermometers.
What is Dry Block Calibrator and how to use it  1

State the Principle of the Dry Block Calibrator:

Woking principle of a dry block calibrator

“Heating up a metal block and maintaining stable temperature”.

Explain parts of the Dry Block Calibrator:

The dry Block Calibrator consists of.

  1. A well-designed insert holes to accommodate a variety of the devices under test called sensors.
  2. Heating coils to raise the temperature.
  3. Internally mounted sensor (RTD or TC) or reference thermometer to measure to indicate the temperature of calibrating devices.
  4. An electronic controller or PID controller for setting and controlling the temperature of the calibrator bath.

What are the factors considered for selecting a Dry Block calibrator?

The following are important factors considered for selecting a Dry Block calibrator

1. Temperature Range:

  •  Select a calibrator that handles a wide range of temperatures usually 1200 Degrees Celsius. Because each calibrator has various temperature ranges.

2. Sensor Size:

  • During the calibration of the temperature sensor using a dry-block calibrator, an immersion length or insertion depth is an important factor to be considered for accurate results.
  • The minimum immersion depth is determined by the sensor diameter and length of the internal sensing element
  • Generally, the minimum sensor immersion depth must be 15 times greater than the sensor diameter and length of the internal sensing element.

3. Batch Size:

  • A wide range of inserts is available for dry block calibrators having more numbers of holes with different sizes.
  • A dry block calibrator can calibrate up to three RTD and Thermistor probes simultaneously.
  • The limiting factor is defined as the total number of sensors that can be inserted simultaneously without a probe handle that touches each other above the dry well.
  • A dry block calibrator can calibrate one to three dozen sheathed thermocouples at a time.
  • Dry block calibrators are more sensitive to sensor loading errors caused by the movement of heat inside and outside of the dry block through sensors that create temperature gradient errors.

4. Work Location:

  • Dry block calibrators are ideal for calibration in the laboratory as well as in field locations. Because these calibrators are portable in size and lightweight. But the safety measures must be strictly considered.

5. Accuracy Requirement:

  • Stability, uniformity, and display accuracy are important parameters needed to consider when selecting a temperature source.
  • The stability of an instrument is defined as the capacity of the source to sustain a constant temperature over time.
  • Whereas, uniformity of an instrument is defined as the capacity of the source to maintain a constant temperature throughout its working area. 
  • Generally, the stability and uniformity of temperature baths are high compared to dry-block calibrators.

How to calibrate RTD or TC using Dry Block Calibrator?

Calibration of RTD or TC using a dry block calibrator is shown below:

  1. Place the reference sensor, and calibrating sensors may be RTD or TC in the calibration bath.
  2. Make sure that the reference sensor is placed at the center of the bath and that all calibrating sensors are placed close together in a radial or circular path.
  3. Connect the test leads of calibrating sensor to the indicator to note the measured value using proper 2-wire, 3-wire, or 4-wire configuration.
  4. Enter the required set point of calibration bath using knobs or keys provided the bath maintains the temperature as per the user settings or requirements.
  5. Measure the temperature of the reference sensor and the temperature of the device under test (DUT) and calculate the resistance using calibration coefficients.
  6. Record the resistance of the device under test (DUT) such as resistance thermometers which are similar to that of reference probe measured in a similar method.
  7. End the calibration process by measuring the reference probe one more time with other temperature values.
  8. Note all the measured data in a table and plot a chart of reference sensor versus device under test in a straight line path.

Various names of a Dry Block Calibrator:

  • Dry Block
  • Dry Block Temperature Calibrator
  • Dry-Well Calibrator
  • Block Calibrator
  • Temperature Block
  • Dry Bath Temperature Calibrator

Specification of Dry Block Calibrator:

Temperature Range300 to 1200  Degrees Celsius
Accuracy±2 Degrees Celsius
Stability±0.1°C at 300 Degrees Celsius ±0.2°C at 800 Degrees Celsius ±0.35°C at 1200 Degrees Celsius
Radial Uniformity±0.15°C at 300 Degrees Celsius ±0.25°C at 800 Degrees Celsius ±0.4°C at 1200 Degrees Celsius
Axial Uniformity1.0°C up to 80mm at 1200 Degrees Celsius
Controlling SensorsR type duplex
Stabilization Time15 to 20 minutes
Immersion Depth160 mm
Insert OD Dimensions37 mm
Controlling MethodSelf-tuned PID controller
Heating Time1.5 Hours
Operating Temperature 20 to 45 Degrees Celsius
Resolution1 Degrees Celsius
DisplayLCD, °C or °F user-selectable
Size (H X W X D) Mm590(H) x 450(W) x 530(D) mm
Weight5 Kilograms
Power Requirements230 V AC, 50 Hz   Single Phase
Computer InterfaceRS – 232
CalibrationAccredited calibration certificate provided
Environmental Operating Conditions0 °C to 40 °C, 0 % to 90 % RH (non-condensing)
Specifications Valid In Environmental Conditions13 ° Degrees to 33 Degrees Celsius

What is a calibration bath?

  • It is a calibrator with a consistent fluid cage or bowl like structure adjusted for specified temperature ranges.
  • The calibration bath offers high volume and is more stable for calibrating temperature sensors of various sizes and shapes.

Some operating and installation guidelines are required to follow:

  1. Do not use these calibrators outdoors (on site), recommended only for use in the laboratory (indoor use).
  2. The operation surface must be clean, stable, and dry.
  3. It should be placed only in a vertical position on an even surface.
  4. Maintain enough space around the calibrator such that there must be at least > 1 m at the front side, more than > 0.5 m at both sides, and there must be sufficient clear space above the calibrator.
  5. Provide enough ventilation area around the calibrator.
  6. Do not operate the calibrator near any kind of flammable materials.
  7. Make sure the calibrator must not be installed in any cupboard, cabinet or bureau self, or other location similar to it.
  8. Do not block or cover ventilation openings.
  9. Calibrator must be installed in such a way that operation must be easy and safe at any time.

What are the Advantages of a Dry Block Calibrator?

Advantages of Dry Block Calibrator:

  • Faster heating up and cooling down.
  • Can be used for higher temperature range.
  • Smaller in size.
  • Light weight such that it can be carried easily.
  • Designed for all industrial applications.
  • Ideal for complete integrated calibration solutions.
  • Can calibrate two to three sensors at a time.
  • Operation is easy through the touchscreen.

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