Common terms Used in DP Transmitter Calibration ~ Learning Instrumentation And Control Engineering Learning Instrumentation And Control Engineering

Common terms Used in DP Transmitter Calibration

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Lower Range Limit (LRL)
This is the lowest value of the measured variable that a transmitter can be configured to measure. This is different from Lower Range Value (LRV)

Lower Range Value (LRV)
Lowest value of the measured variable that the analog output of a transmitter is currently configured to measure.

Transmitter Re-ranging
Configuration function that changes a transmitter 4mA and 20mA settings

Upper Range Limit (URL)
This is the highest value of the measured variable that a transmitter can be configured to measure. This is different from Upper Range Value (URV)

Upper Range Value (URV)
Highest value of the measured variable that the analog output of a transmitter is currently configured to measure

Span
Span is defined as the algebraic difference between the upper (URV)and lower range(LRV) values of the DP transmitter.

Span = URV – LRV
For example, if the DP transmitter is being used to measure a pressures in the range 0 – 300psig, then URV = 300, and LRV = 0
Therefore span = URV – LRV = 300 – 0 = 300
To have a better understanding of LRV and URV as used in instrumentation systems, please go through control signals

Calibration Range
The calibration range of a DP transmitter is defined as “the region between the limits within which a quantity is measured, received or transmitted, expressed by stating the lower and upper range values.” The limits are defined by
the zero and span values of the DP transmitter. The zero value is the lower end of the range. For example a DP transmitter being used to measure pressures of 0 – 500 psig has a calibration range of 0 – 500 psig.

Instrument Range
This refers to the capability of the DP transmitter. If a manufacturer has designed a DP transmitter for the range 0 – 700psig for example, then 0 – 700 psig is the instrument range of the transmitter. Under no circumstances should the DP transmitter be used in an application where the pressure is expected to be above 700psig as this will inevitably destroy the transmitter because its capability has been exceeded.

The calibration range may be the same or differ from the instrument range. For example, a DP transmitter may have a nameplate instrument range of 0–700 psig and output of 4 - 20 mA. However, if an engineer has determined the instrument will be calibrated for 0-to-300 psig = 4-to-20 mA. Then, the calibration range would be specified as 0-to-300 psig = 4-to-20 mA. In this example, the zero input value is 0 psig and zero output value is 4 mA. The input span is 300 psig and the output span is 16 mA.

MWP
MWP means the Maximum Working Pressure of the DP transmitter. MWP refers to the amount of gauge pressure common to each port (High and Low ), not the differential pressure between ports, that the DP transmitter can safely handle without being damaged.

Transmitter Damping
Output function that increases the response time of a transmitter to smooth the output when there are rapid input variations

Zero Trim
A zero-based, one point adjustment used in different pressure applications to compensate for mounting position effects or zero shifts caused by static pressure.