ABB Data Sheet ControlIT Harmony Analog I/O
The Harmony Input/Output (I/O) System utilizes a variety of input and output blocks to inter face process signals to the Symphony ™Enterprise Management and Control System. Analog
input (AIN) blocks interface field inputs such as pressure and flow transmitter signals, thermo couple (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.
Operation
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 func tion 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.
Digital Signal Processing
The AIN-120 block uses a floating point digital signal processor (DSP) to achieve low pass filtering. The advantage to using a DSP device for this function is that significant noise rejection can be
achieved (better than 70 dB) while maintaining fast settling time to an input step response (75 milliseconds). As stated previously, the Delta-Sigma analog-to-digital converters used in the AIN-200,
AIN-220, and AIN-300 blocks have built-in digital signal processing which provides low pass
filtering.
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.
Current Limiting
The analog input channels provide onboard current limiting for short circuit protection. The current limiting prevents circuit damage that can result from excessive current levels at an input
channel caused by field input faults. Specifically, the four to 20 milliampere input channels are
protected against shorts across the transmitter, across positive and negative terminals, from the
positive terminal to ground, and from the negative terminal to ground. A channel will recover to
full function after correcting the fault condition.
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.
Calibrations
The electronics automatically adjust analog outputs to compensate for supply voltage variations.
Field calibration of analog outputs is not required.
Readback
Each analog output channel is monitored on the block. This readback function serves two
purposes:
■ Provides high accuracy (0.1 percent) by using a software compensation algorithm in combination with the analog output readback value.
■ The integrity of the hardware and field wiring is constantly monitored by way of checking
the readback value.
The block also reports the readback values to the controller. It automatically scales the values to
their proper engineering units before reporting them. The readback values are converted to the
proper engineering units based on engineering unit high and low value specifications.
Analog Input Blocks
The AIN block interfaces various analog inputs: Current, voltage, thermocouple, and RTD. An
AIN block that supports thermocouple inputs includes cold junction compensation for the TC
inputs and can detect open thermocouples. The AIN block supports redundant I/O electronics.
An AIN block can be ordered with either a screw terminal (S type) or cable/clamp terminal (C
type) base.
AIN-120
Current, High Level Voltage In
The AIN-120 block supports the following inputs:
■ 4 to 20 milliampere.
■ –10 to +10 VDC differential.
■ –10 to +10 VDC single-ended.
The block provides 16 nonisolated input channels that are individually hardware configurable for
either voltage or current mode and software configurable for voltage range.