1
Chapter
1
About the FLEX I/O HART Analog Modules
What This Chapter Contains
Read this chapter to familiarize yourself with the input and output analog modules.
For Information About
What the FLEX I/O Analog I/O
Modules Do
How FLEX I/O Analog Modules
Communicate with Programmable
Controllers
Physical Features of Your Analog I/O
Module
Chapter Summary
See Page
1-1
1-2
1-3
1-8
What the FLEX I/O Analog
I/O Modules Do
The 1794 HART input and output modules must be used in a ControlNet or
EtherNet network.
The 1794-IE8H module accepts up to 8 analog inputs. The inputs are nonisolated and will accept current in either of the following two ranges: 4 to
20 mA or 0 to 20 mA. The default input range is 0 to 20 mA. The inputs have both fixed hardware filters and selectable firmware digital filters.
Similarly, the 1794-OE8H module provides as many as 8 analog outputs. The outputs are nonisolated and will provide current in either of the following two ranges: 4 to 20 mA or 0 to 20 mA. The default output range is 0 to 20 mA.
Each module offers:
• local microprocessor intelligence for advanced features.
• full functionality without switches or jumpers.
• multiple data ranges that can be independently programmed in channel groups.
• lead breakage detection.
• overrange/underrange alarms.
• remote transmitter alarm.
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1-2 About the FLEX I/O HART Analog Modules
How FLEX I/O Analog
Modules
Communicate with
Programmable Controllers
FLEX I/O analog modules provide best utility when used with ControlNet products on the ControlNet network. Data connections are established between the I/O module and an Allen-Bradley programmable controller
(PLC) to transfer information between the two at a scheduled rate.
Input module information is then automatically made available in the PLC data table through the data connection. Reciprocally, output data information determined by the PLC program is also automatically transferred from the
PLC data table to the output module through the data connection.
In addition, when the data connection is originally established, configuration information for the module is automatically transferred to it via the network.
Events Following Power-up
You must apply +24V dc power to your FLEX I/O analog I/O modules. The following sequence of events occurs after power has initially been applied to your module:
1. The module begins an internal diagnostic check. The channel 0 indicator turns ON to indicate the check has begun. The indicator turns OFF when the check is finished.
2. After the diagnostic check, module configuration information, selected by the user and downloaded over the network, is applied by the module.
For more information on configuration options, see Chapter 2.
3. Following the module configuration download for the 1794-IE8H module, the module begins producing runtime data for the PLC processor.
Following the module configuration download for the 1794-OE8H module, the module applies configuration data to output channels.
4. If any diagnostics or alarms are generated during normal module operation, the data is returned to the PLC processor.
Publication 1794-UM063A-EN-P - March 2006
About the FLEX I/O HART Analog Modules 1-3
Physical Features of Your
Analog I/O Module
The module label identifies the keyswitch position, wiring and module type. Use the removable label to note individual designations per your application.
Indicators
Indicators are provided to identify input or output fault conditions, and to show when power is applied to the module. For example, the 1794-IE8H module is shown below.
1794-IE8H
Module Type
Removable Label
I/O
1794-IE8H
8 CH HART ANALOG INPUT
IN0 IN1 IN2 IN3 IN4 IN5 IN6 IN7
PWR
3
Keyswitch Position
Indicator (#3)
Power On Indicator
Input Designators 42054HART
Use Alarms on the
1794-IE8H Module
The 1794-IE8H FLEX I/O module is capable of generating four alarms:
• Underrange
• Overrange
• Remote Fault
• Local Fault
These alarm conditions are described in general terms and as they relate to bits on the FLEX I/O module on the following pages. The following graphic shows at what values these alarms are generated for Data Format 4.
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1-4 About the FLEX I/O HART Analog Modules
Data Format Alarm Example
In this example, the normal active data range is 4-20 mA. The alarms are generated in three overlapping bands.
0 mA
Remote Fault
Underrange
Local
Fault
PHYSICAL INPUT SIGNAL RANGE
4 mA 20 mA
-25.00% -12.50% Programmable in 20 0.1 mA steps by Error
Level 0.1 mA
Steps parameter
0.00% 100.00%
Remote Transmitter Error
Up/Down parameter determines which of these is active
Overrange
Programmable in 20 0.1 mA steps by Error
Level 0.1 mA
Steps parameter
22 mA
Remote Fault
Local
Fault
112.50%
41666
Overrange Alarm
The overrange alarm notifies you when module input is overrange. When the input signal exceeds 100% (20 mA), an Overrange Alarm is generated.
This alarm stays active at any value above 100% of range and is always enabled by the module.
Underrange Alarm
The underrange alarm works converse to the overrange. This feature notifies you when the input signal falls underrange. If the input signal falls below 0% (4 mA), an Underrange Alarm is generated.
This alarm stays active at any value below 0% of range and is always enabled by the module.
Publication 1794-UM063A-EN-P - March 2006
About the FLEX I/O HART Analog Modules 1-5
Remote Fault Alarm
The remote fault alarm is intended for use with remote transmitter loops.
For example, the remote transmitter may be measuring temperature and converting it to a standard mA signal. In such a loop, though, the input module cannot determine the state of the loop on the far side of the transmitter.
However, the remote transmitter may be capable of diagnosing a problem in the remote loop and signal the input module local loop with a preprogrammed out of range (high or low) value.
The remote fault alarm allows the 1794-IE8H module to work with transmitters like the one just described. You must use the Remote Transmitter
Error Up or Down feature, see page 2-2, to configure your application for
Remote Fault notification.
For example, you must determine if you want a remote fault to cause high out-of-range values or low out-of-range values to be returned to the controller.
IMPORTANT
Once the alarm is issued, it remains active as long as the input signal value remains above the programmed value.
Use Remote Fault Alarm to Determine High-High or Low-Low Alarm Levels
If you do not have a remote transmitter in your loop, this alarm can also be used to program a high-high or low-low alarm level between the levels which actuate the overrange or underrange alarms and the high or low local fault alarms.
IMPORTANT
When establishing high-high or low-low alarms, you can only select one side (high or low). You must use the Remote
Transmitter Error Up or Down feature in conjunction with this alarm.
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1-6 About the FLEX I/O HART Analog Modules
Programming the Remote Fault Alarm
For the remote fault alarm, you must program the threshold in 0.1 mA steps at any level on the high or low end of input signal range. The remote fault alarm activates if your I/O module receives input signal values of:
• 100.63 to 111.88% (20.1 to 21.9 mA) on the high end of input signal range or
• -0.63 to -11.88% (3.9 to 2.1 mA) on the low end of input signal range
IMPORTANT
This alarm is only active for one band, either on the high side of normal operation or the low side.The Remote Transmitter Error Up/Down parameter
determines which side is active. See page 2-2 for a description of the
Remote Transmitter Error Up/Down feature.
Local Fault Alarm
The local fault alarm notifies you when the loop to the transmitter or field device, if no transmitter is used, is open or shorted.
IMPORTANT
Once the alarm is issued, it remains active as long as the input signal value remains in the programmed range.
• 112.50% (22 mA) or higher on the high end of input signal range.
This value indicates a short in the loop.
or
• -12.50% (2 mA) or lower on the low end of input signal range.
This value indicates an open wire condition in the loop.
The remote fault and local fault alarms are issued with the same bit whether the cause is an under or overrange. Monitor the overrange and underrange bits in your programming software to determine if the problem is a high current or low current.
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How to Use the
HART Capabilities
HART Implementation
Overview
About the FLEX I/O HART Analog Modules 1-7
Before using the HART capabilities, be sure that:
• the I/O module and the associated field device are working properly in the analog 4 to 20 mA mode.
• the I/O module is configured for 4 to 20 mA range.
• the field device is HART capable.
• no more than one HART field device is connected to each channel.
• input filtering is set to a valid (defined) value.
The FLEX I/O HART modules act as intelligent HART multiplexers.
Basically, the module learns which HART devices are attached to its channels and then routes HART messages, as appropriate, between the HART field devices and the flexbus. Since the HART modules act as intelligent HART multiplexers, HART commands can be issued to the HART modules themselves.
Communication on the flexbus occurs between the adapter and the HART module. The adapter converts these messages to the appropriate network format for communication with the controlling processor. The controlling processor gets its command from the user program, storing the responses in its memory.
Processor
User Program
Command
For Example,
ControlNet
Adapter
Response
Flexbus
FLEX I/O
HART I/O
Module
4 to 20 mA
HART
Field Device
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1-8 About the FLEX I/O HART Analog Modules
Chapter Summary
In this chapter, you learned about FLEX I/O analog I/O modules and HART module capabilities. Move on to Chapter 2 to learn about configurable features on your module.
Publication 1794-UM063A-EN-P - March 2006
