ABB WBPEEUD240001A2 Harmony Analog I/O

ABB WBPEEUD240001A2 Harmony Analog I/O 

Description

The Harmony Input/Output (I/O) System utilizes a variety of input and output blocks to interface process signals to the Symphony ™Enterprise Management and Control System. Analog  input (AIN) blocks interface field inputs such as pressure and flow transmitter signals, thermocouple (TC) inputs, and resistive temperature device (RTD) inputs. Analog output (AOT) blocks  provide output signals to adjust final control elements such as control valves, pumps, positioners,  actuators, etc. These analog blocks along with other types of blocks for digital and control I/O  interface and remote I/O communication combine to create a complete I/O system (Fig. 1). Refer  to the Harmony Input/Output System overview for a complete system description.

Each analog I/O block has an onboard microprocessor which controls and performs the following  functions for the block:

■ Hnet communication. 

■ Analog input/output processing. 

■ Redundancy link communication. 

■ Block diagnostics. 

■ Status reporting.

Along with these functions, the microprocessor is also responsible for executing the I/O block  portion of the control configuration. The complete control configuration made up of linked function codes resides and is retained in the Harmony controller at all times. The controller only off  loads a portion of the configuration to be executed by the individual I/O blocks.

Function codes are predefined, fixed function algorithms. When interfacing analog I/O blocks, the  controller utilizes the following function codes:

■ I/O device definition (FC 221). 

■ Analog input/channel (FC 222). 

■ Analog output/channel (FC 223).

Specifications are set on a per channel basis rather than on an I/O group basis. The function codes  provide addressing, and start-up, execute (i.e., run time), override, simulation, and failure mode  operation specifications. The I/O channel function codes are exception reporting function codes.

Analog Input

The Harmony I/O System supports four to 20 milliampere, high level –10 to +10 VDC, low level  -100 to +100 millivolt (DC), thermocouple (TC), and resistive temperature device (RTD) inputs  through AIN blocks:

■ AIN-120 - High level voltage, current in. 

■ AIN-200 - Isolated TC, high level voltage, low level voltage in.

■ AIN-220 - Isolated TC, high level voltage, low level voltage, current in. 

■ AIN-300 - Isolated RTD in.

Data Conversion

An AIN block reads currents or voltages at its input channels, scales and converts the inputs to  real values in engineering units, then reports the input values to the controller. The block provides  channel status information along with each reported input.

High and low level inputs are converted to the proper engineering units based on input type and  engineering unit high and low value specifications. Thermocouple and RTD inputs are converted  to the proper engineering units (degrees C or degrees F) using predefined conversion tables for  each type of thermocouple and RTD supported.

The AIN-120 block uses a single successive approximation analog-to-digital converter through  which all channels are multiplexed. This type of A/D conversion method is fast (ten microseconds  per conversion), which allows multiple channels to be sequentially multiplexed through one converter. Redundancy provides a backup analog-to-digital conversion.

The AIN-200, AIN-220, and AIN-300 blocks have dedicated Delta-Sigma analog-to-digital converters on each channel. These converters are slower (50 milliseconds per conversion); however,  no multiplexing is required since each channel performs independent conversions. The converters  also have built-in digital signal processing which provides low pass filtering. The AIN-200,  AIN-220, and AIN-300 blocks have optically isolated input channels.

Calibrations

No field calibrations are required. The electronics automatically perform the following adjustments to the raw analog inputs depending on input type:

■ Drift correction using onboard zero and span reference voltages. 

■ Lead wire resistance adjustment for low level, thermocouple, and RTD inputs. 

■ Cold junction temperature compensation for thermocouple inputs using either an internal or  external cold junction reference.

Analog Output

The Harmony I/O System supports four to 20 milliampere outputs through an AOT-150 block.  This block receives output demand values in engineering units from the controller, scales the  demand values to percentages of output, and converts them to analog voltages or currents at the  output channels. User selectable default states of zero percent, 100 percent, or hold output are  provided.