Setup of Analog Inputs in Accord Builder
An Analog Input is a signal received by the PLC which represents an analogue value,
Analog Inputs are items such as Level Transmitters, Pressure Transmitters, VSD Actual Speeds and signals from other PLC’s,
Following insertion in a unit, an analog input is configured with settings that will determine its operation and its description in documentation. During insertion, the input is given a name and short description. The name may be changed at any time.
There are three tabs in the analog input properties configuration section. The name, units and range of the input are given in the Current Item section. Cross reference, Save and Close buttons are also provided.
The following aspects of the device must be filled as required: Address: This is the channel address of the instrument, in the PLC. Input Type: This refers to the type of connection to the PLC, which will affect the scaling routine. The following types are configurable:
- Electrical Input e.g. 0-5 V, or 4-20 mA
- Bus based Input – Real – The signal is read from Bus channel with applied Scaling Factor.
- Bus based Input – Word (Integer) – The signal is read from Bus channel with applied Scaling Factor.
for Electrical Inputs:
Min Range: This is the lower value of the range in engineering units that the Electrical Input is to be scaled between.
Max Range: This is the upper value of the range in engineering units that the Electrical Input is to be scaled between. for Bus Based Inputs:
Scaling Factor: The Factor applied to Bus Based Inputs to obtain Engineering Units.
To derive process alarms the following may be assigned:
Alarm Value HH: High-High Setpoint – This is the setpoint at which the High High Alarm occurs.
Alarm Value H: High Setpoint – This is the setpoint at which the High Alarm occurs.
Alarm Value L: Low Setpoint – This is the setpoint at which the Low Alarm occurs.
Alarm Value LL: Low-Low Setpoint – This is the setpoint at which the Low Low Alarm occurs.
Alarm Delay Time: This is the time in seconds that must elapse before an Alarm is triggered. The scaled value in engineering units must be greater than or less than the respective setpoint for this time.
Hysteresis: This is the value that the scaled value must recover by in order to release the alarm point.
Example – If the high alarm is set to 90 and the alarm timer is 5 seconds and the hysteresis is set for 2 then the high alarm will be set if the analog input scaled value exceeds 90 for 5 seconds continuously. The high alarm will only be released as soon as the value falls below 88.
Indication Only: Analog Inputs are usually referenced in Programs or PID Loops. This option is used if the item is only required to be monitored and displayed. This allows the item to pass consistency check if it is not referenced by PID or program item.
Enable Wirebreak Alarms: This is used to enable WireBreak checking and to cause an equipment Alarm if the signal fails. This is only for Electrical Inputs.
Place Unit/Program In Error: if a Wirebreak occurs then the Equipment Unit will be in Alarm, and consequently any programs using the Unit will be in Alarm.
IQ Information – this information is used in the automatic generation of the IQ document
Tolerance: This is the error allowed for a particular reading. It is in terms of the scaled engineering units value.
No. of Points: This is the number of readings that are to be tested during the IQ.
The IQ information fields are used to supply information for the IQ document.
In the IQ document a table is produced. Each row in the table is a test for the analog instrument. The number of rows is given by the No. of points above in the IQ set-up area. The Max and Min are always included and the other points are evenly spaced in the range e.g. an instrument of range 0 to 100 with 5 test points will be tested at 0, 25, 50, 75, and 100.
For each test point a tolerance is applied. This tolerance is the error that can be tolerated in order for the instrument to pass the test at that point.
The standard Siemens scale is 0 to 27648. The raw value being read by the PLC from the instrument item may be monitored in the register status area of Accord Builder.
The tolerance value input at Accord Builder is used to derive the equivalent value in terms of the raw value. This max raw value error is then shown in the table. The recorded value observed from the PLC must be within the raw value error in order for the instrument to pass the test.
E.g. An instrument of range 0 to 100 – the mid-range point of 50 would correspond to 27648 divided by 2 or 13824. If a tolerance of 1 is applied the possible error is limited to 276. The raw value being read from the instrument must be between and 13548 (13824-276) and 14100 (13824+276).
Card Setup Tab:
A PLC is composed of a CPU and I/O cards on racks, and in some cases communications processors, special function modules and bus based I/O.
Panel, Central Rack, Slot and Channel: These are all text input fields. Once a text is entered for a device or instrument, it then becomes available for other objects in the project. There is no validation on this information; the same combination of information could be entered for more than one device. This would be erroneous as each device must be unique, so care must be exercised in inputting the information. This can be filled in the IO Table in the Menu.
Type: The type of electrical signal associated with the analog input is also described in this tab. In this case a 4-20 mA – 2 wire signal is identified, which corresponds to a setting of C in the PLC measuring module. The information stored in this area is used for documentation and does not comprise object data for PLC control.
The following aspects of the device may be filled in if required:
Symbol: This may be an asset number or any unique identifier which describes the object within the entire company. This could contain references to the plant, the area within the plant, the unit and the digital input name itself.
Part Number: This is the supplier reference for the item.
Type Description: This is a general description of the type of item. If a type is entered, then it becomes available to all other objects of the same type.
Long Description: This describes the object in more detail, if required.
Supplied By: Name of the supplier.
Notes: General Notes on the object. This may contain reference to maintenance manuals, maintenance history or location and type of spare parts.