Delta Controls 2HT - Manual (Page 5)

002522-2HT 180210.doc 5
PRODUCT INTRODUCTION
The Delta HT Series of SMART transmitters accurately measures gauge or absolute pressure and
transmits a traditional 4-20 mA signal as well as a digital signal using the HART® protocol. The HART®
protocol gives the ability to
integrate into one system, products from different manufacturers with
predictable functionality and control. HART® has become the most widely used digital communication
system for process instruments and controllers.
These transmitters complement the popular Delta 387 transmitters. Digital technology has been used to
ensure accuracy, stability and range-ability across the full temperature range. Like its smaller brother the
HT series of transmitters features a robust all stainless steel case.
The extensive use of surface-mount components and custom micro-power devices has resulted in a
transmitter that is small, light and self supporting, although pipe mounting brackets are available if
required.
In addition to the remote digital communications, the unit has, as standard, local zero and span
adjustment at the touch of a button. If more than just local span and zero are required, there is a local
display module available, the D-CAL. This can directly access more than 80% of the SMART
transmitter’s commands, for installation, commissioning and maintenance checks. The display may be
fitted within the unit with no change to the external dimensions or supplied in a small hand-held case for
repeated use when configuring blind instruments.
The transmitter is manufactured within a quality system, approved to ISO 9001:2000.
FEATURES
THE SENSOR :-
Gauge and Absolute Pressure - The preferred sensor below 10 Bar is a precision piezo-resistive
transducer, with a silicone fill and a 316 stainless steel diaphragm. Above 10 Bar the sensor is a one
piece, machined diaphragm with a sputtered thin film strain gauge. The diaphragm is specially designed
to optimise the sensor for each range. The wetted parts of the sensor (diaphragm and inlet) can be
selected from stainless steel, Monel or Hastelloy C
to suit the process fluid being used. Gauge or
absolute reference can be offered on all ranges.
THE ELECTRONICS :-
The heart of the HT transmitter is an electronics module that uses surface mount technology
and a 16 bit micro-controller, supervising all functions of the transmitter and performing
continuous self checks to make sure the software is running properly.
The micro-controller takes the digital output from the sensor electronics and, using calibration
coefficients, compensates the sensor signal for linearity and local temperature. Because the actual
pressure is now digitised, any mathematical function may be applied to change the output. This allows
conversion between different engineering units to be shown and square root extraction to be applied
where required.
Any changes to the transmitter configuration are stored in EEPROM which is non volatile in the event of
power supply failure. If a power failure occurs the transmitter will restart safely and signal digitally to a
controller that a power failure has occurred.
The digital, linearised signal is fed to the output circuits. One signal is converted into a 4 to 20 mA
current, the other is a superimposed audio tone conforming to the HART® protocol.
The input and output circuits of the transmitter are fully protected against over voltage, reverse polarity
and RFI ; the local display/configurator is IP rated and protected against RFI.
THE SOFTWARE :-
The software controls all functions of the transmitter, continuous self-diagnostics, communications,
pressure calculations and display (if fitted). The firmware program is permanently stored within the
micro-controller, all calibration and run time variables are stored in EEPROM. The software has built-in
checks for sensor failure, loss of voltage reference and many other very unlikely failures. The software
also contains complex algorithms for temperature and sensor linearisation, to mathematically
characterises the sensor and electronics over its full temperature range to guarantee accuracy and
repeatability. Within the software there is also a powerful state machine which is the set of statements
that make decisions within the local configurator, and allows the transmitter to be set up as required.