Analog to Smart Transmitters Flashcards
Pneumatic transmitter that measures process sensor variable and converts the value into a proportional value into a standard output signal (3-15 psi, 20 to 100kPa)
Analog Transmitter
Electronic transmitter that uses operational amplifiers circuitry to convert process sensor variable to a proportional current output (4-20 mA)
Analog Transmitter
Sensor analog value is converted to digital value that is fed to a microprocessor for processing then the digital signal is converted back to analog output (HART)
Digital Transmitter
digital value after sensor is used as digital signal output (Foundation Fieldbus, Profibus etc)
Digital Transmitter
Analog Outputs
Process output in standard format (3-15psi, 4-20mA etc)
Electronic output (4-20 mA) with HART and other Digital Outputs (FF)
Digital Outputs
Limited, requires numerous transmitters to cover all values
Analog Input range
Larger turndown ratio’s Fewer transmitters required
Digital Input range
Analog Re-range
Need to re-calibrate to change range
Entered with communicator(or PC) Relatively fast
Digital Re-range
Input known value, interactive Zero & Span adjust screws
Analog Calibration
Digital Calibration
Input known value, non- interactive Zero-Lower-Upper Trim
Analog Accuracy
Good accuracy, temp Press effects output
Good accuracy, temp.-press. effects compensated for
Digital Accuracy
No diagnostics onboard, needs to be checked
Analog Diagnostics
Transmitter able to communicate its “health” back to user
Digital Diagnostics
Limited number available, generally not in production
Analog Availability
Common among all manufactures, readily available
Digital Availability
The set of rules defining a format is called a
protocol
– HART
– MODBUS
– FOUNDATION FIELDBUS
– PROFIBUS
Examples of Instrumentation Protocols
HART is an acronym for what?
Highway Addressable Remote Transducer
Protocol for sending and receiving digital information across analog wires between smart devices and control or monitoring equipment
HART
List five reasons to use a smart device
Device Configuration or re-configuration Device Diagnostics Device Troubleshooting Reading the additional measurement values provided by the device Device Health and Status
The HART Protocol communicates at
1200 bps
HART primary/secondary protocol mean
which means that a smart field (secondary) device only speaks when spoken to by a primary
HART signal interrupts the 4-20 mA output signal of a device
FALSE
device status, diagnostics, additional measured or calculated values, etc
device information carried on the digital HART signal
benefits of using HART Communication
Leverage the capabilities of a full set of intelligent device data for operational improvements.
Gain early warnings to variances in device, product or process performance.
Speed the troubleshooting time between the identification and resolution of problems.
Continuously validate the integrity of loops and control/automation system strategies.
Increase asset productivity and system availability.
Increase Plant Availability
Reduce Maintenance Costs
Improve regulatory compliance
HART-Device Description
an electronic data file prepared in accordance with Device Description Language specifications
HART Device Description Language (DDL)
language to describe devices
