Most instruments and sensors are designed to meet certain accuracy specifications; the process of adjusting an instrument to meet those specifications
is referred to as calibration. The device used to calibrate other instruments is known as a calibrator. Calibrators vary in form and function depending on the
instruments with which they are designed to work. Several different types of calibrators are described below.
Types of Calibrators
Black Body Calibrators
A black body is used for calibrating infrared pyrometers. They typically consist of a target plate that has a
very high emisivity. The temperature of the target plate can be controlled to very tight tolerances. To calibrate and infrared pyrometer, the pyrometer makes a
measurement of the the target plate. The controlled temperature of the plate is compared with the pyrometer reading. The pyrometer is then adjusted until the
the difference is minimal. The high emissivity of the target plate minimizes emissivity errors.
Block Calibrators are used for calibrating temperature probes. They contain a metal block that can be heated to a precise temperature. Temperature probes can
be inserted into the block and the measured temperature of the probes can be compared with the controlled temperature of the blocks. Since temperature
probes generally don't have any adjustments, this is really verification process rather than a true calibration.
Simulators and Signal References
When calibrating an instrument, such as a panel meter or temperature controller, it is necessary to input a precise known electrical signal.
The instrument's display or output value can then be adjusted to match the input signal. a signal reference is used to generate the precision
signal. Signal references are available as voltage references, current references and frequency references. When working with an instrument that
reads a sensor, such as thermocouple, a special type of signal reference, called a simulator is used. The simulator can accurately reproduce
a sensor output. Many signal references and simulators can not only generate signals but read them as well.
Fluidized Sand Bath Temperature Probe Calibrators
Fluidized baths provide safe, rapid heat transfer and accurate temperature control, enabling you to
efficiently and safely calibrate and maintain temperature sensitive instruments.
The principle of fluidization occurs when a gas usually low pressure air or nitrogen flows upward through a partially-filled chamber or retort of dry,
inert particles of aluminum oxide. The gas flows at a low velocity, which sets the particles in motion, separates them, then suspends them to a stable
level to give the particles the appearance of turbulence quite similar to the state of boiling liquid.
Besides circulating and flowing like a liquid, fluidization solids exhibit excellent heat transfer characteristics. Temperature probes inserted
into the bath come to a consistent, stable temperature very quickly.
ice point™ Calibration Reference Chambers
ice point™ calibration reference chambers employ thermoelectric cooling elements to produce
a very precise stable 0°C reference chamber. The reference chamber can be used for calibrating temperature probes but they are also
commonly used in simulating a thermocouple signal for the calibration and verification of instruments that read thermocouples.