In digital mode, any transmitter can be accurately re-ranged from any point on the RS485 network without the need to physically access it to apply pressure.
During factory calibration, a table is generated that uniquely characterises each iCT over its full pressure range. This table is compensated for the effects of temperature, non-linearity and hysteresis, and is stored in the transmitter’s non-volatile memory. Unlike conventional analogue transmitters where the 4-20mA output is dependant on the sensor’s displacement, it is possible to assign the 4 and 20mA points anywhere on this table. The user simply enters the pressure values at which 4mA and 20mA outputs are required and accurate recalibration is complete.
The iCT incorporates a 12-bit ADC feedback circuit which constantly monitors the 4-20mA loop. The micro-controller compares its value with the digital signal and the user set calibration and ensures that it is accurate. If, under fault conditions, errors are beyond dynamic correction, an error “flag” is set within the iCT which can be read via the digital output. In addition and if required, the 4-20mA current output may be driven to a pre-determined fixed value. This option is user selectable, as is the actual current value within the limits 3 to 22.5mA.
In digital mode the transmitter also provides a process temperature measurement accurate to within +/- one degree centigrade.
For tank volume or any other applications requiring linearisation, iCT can be programmed with a 20-point look-up table, providing a direct output in volumetric rather than level terms.
All configuration information in the iCT is stored in non-volatile re-programmable memory.