T280, HART adapter with analog input

19/04/2015

T280, HART adapter with analog input

The T280 is an OEM transmitter circuit board that provides HART transmitter functionality.

T280 includes two differential input channels with A/D conversion. Bridge sensor elements may be directly connected to T280.  Application specific front-end electronics may easily be connected. 6 mA is available. T280 supports Universal, a selected set of Common Practice HART commands and
Device Specific commands for sensor trimming and factory configuration by an OEM user. T280 is compliant with the HART 6.0 standard. T280 is suited for a two-wire loop powered design. T280 supports HART multidrop configuration. T280 supports HART burst mode communication.

General description:

T280 contains a four channel 24 bit A/D converter from Texas Instruments. The circuit board comprises a Texas MSP µcontroller that runs the protocol and the application.

T280 supports the HART Universal and the most applicable Common Practice Commands and can consequently be configured from any HART compliant hand held communicator or PC configuration tool.

T280 also provides several Device Specific Commands that allow the OEM customer to configure and trim the circuit board in the factory. There are commands for setting addresses, serial numbers, and sensor limits and for calibrating the sensor.

T280 supports three different input channels that can all be configured to be the Primary Variable (PV). Channel one and/or two could be a sensor bridge. It provides constant current or constant voltage for feeding the bridge.

There are connections for an LCD display and push buttons. These allow implementation of a local display. The display will show the measurements in digital values and as a bar graph. The easy to use configuration menu controlled from three buttons allow configuration of all essential HART functionality. It is easy to expand with custom specific menus.

Applications

The T280 is intended for embedding in field transmitters. It supports various measurement applications. The circuit design and component selection are targeted to allow rough industrial use. It comes in two variations, generic measurement and pressure bridge sensor application. The latter version allows temperature compensation and linearisation of the bridge.

T280 features:

  • 24-bit resolution (sigma-delta A/D)
  • Programmable gain in preamplifiers (1 – 128 times)
  • 2 kbyte for programmable non-volatile configuration memory (Personality PROM)
  • 3.3 V regulated supply
  • The sensor input range may trimmed
  • Device addresses can be programmed
  • Reference voltages at 1.25 V
  • Circuitry for IS protection
  • Circuitry for EMC protection

T280 specifications:

  • Mechanical size round card 65 mm
  • Mounting three 3 mm screws
  • Operating temperature range -40 °C to + 85 °C
  • Max input signal range 10mV to 1.25 V
  • Input supply voltage range 12-39 -Vdc
  • The HART Universal and Common Practice commands
  • SW drivers for personality PROM and A/D converters
  • Input signal unipolar or bipolar
  • 6.0 mA available for sensor use

HART Commands included:

All Universal Commands

  • All Common Practice commands required by the application
  • Selection of range
  • Selection of engineering units
  • Programming of the filter constant
  • Selection between linear and square root transfer function
  • Burst mode control

Devices specific commands for device configuration, two point trimming of sensor and A/D programming are supported.

Commands and functions for sensor liinearisation and temperature calibration may be added on request.

Engineering Unit and conversion between these are included for a variety of unit classes such as pressure, temperature, mass flow and volumetric flow applications. Other Engineering Units can be included on request.

Profiles

The module may be used for a wide variety of measurement applications. There are special profiles for:

  • Pressure
  • Temperature
  • Mass flow
  • Volume flow
  • Level

Sensor interface specifications:

Sensor input, unipolar
(Programmable ranges – mV)
0 – 1250 mV            (default)
0 – 9.75, 0 – 19.5, 0-39, 0-78, 0-156, 0-313,0-625, 0-1250

Sensor input, bipolar
(Programmable ranges – mV)
 +/- 78 mV
 +/- 9.75, +/- 19.5, +/- 39, +/- 78, +/- 156,+/-313, +/-625, +/- 1250

Resolution of the ADC input channels
24 bits

Temperature drift of Channel 1 and 2
<  25 ppm/°C

Supply voltage for application electronics
3.3 Vdc  +/- 5%

Maximum current available for application electronics
6.0 mA

Constant current output for feeding of sensor bridge
Up to 4.0 mA

Constant output voltage for voltage drive of sensor bridge
3.3 Vdc

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