Introduction to Smart Transmitters

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Smart Transmitters are advancement over conventional analog transmitters. They contain microprocessors as an integral unit within the device. These devices have built-in diagnostic ability, greater accuracy (due to digital compensation of sensor nonlinearities), and the ability to communicate digitally with host devices for reporting of various process parameters.

The most common class of smart transmitters incorporates the HART protocol. HART, an acronym for Highway Addressable Remote Transducer, is an industry standard that defines the communications protocol between smart field devices and a control system that employs traditional 4-20 mA signal.

Parts of a Smart Transmitter:
To fully understand the main components of a smart transmitter, a simplified block diagram of the device is shown below:

Fig A: Basic parts of a Smart Transmitter

The above block diagram is further simplified to give the one below:

Fig B: Simplified block diagram of a Smart Transmitter

As shown above in fig A, the smart transmitter consists of the following basic parts:

Basics of Flow Measurement with the Orifice Flow Meter II

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Accuracy and Rangeability of Orifice Metering Systems. 
The performance of the orifice meter system just like other differential pressure flow meters depend on the precision of the orifice plate and the accuracy of the differential pressure sensor. Orifice plate accuracy is rated in percentage of actual flow rates whereas the differential pressure transmitters have their accuracy rated in percentage of calibrated span. Due to the fact that flow rate is proportional to

Basics of Flow Measurement with the Orifice Flow Meter I

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The differential pressure measurement method is a universally utilized measuring principle for flow measurement. The orifice flow meter is a type of differential pressure flow meter that can be used for measuring gases and liquids.

As shown in Flow Instrumentation: principles and Formulas, we know that the relationship between flow and differential pressure in a flow restriction device like the orifice meter is given by:

$Q = K\sqrt{\frac{\Delta {P}}{ρ}}$

Where
k = a constant
ΔP = differential pressure across device
ρ = density of the fluid.

In the above formula, fluid density is a key factor in flow measurement computation in both liquids and gases. If fluid density is subject to change over time, we will need some means to continually calculate ρ so that our inferred flow measurement will remain accurate. Variable fluid density is typically experienced in gas flow measurement, since all gases are compressible by definition. A simple change in static gas pressure within the pipe is all that is needed to make ρ change, which in turn affects the relationship between flow rate and differential pressure drop. Therefore in gas flow measurement, change in fluid density with static pressure is compensated for.