Dual-channel Input Start (DCSRT)
This instruction applies to the Compact GuardLogix 5370, GuardLogix 5570, Compact GuardLogix 5380, and GuardLogix 5580 controllers.
The Dual-channel Input Start instruction is for safety devices whose main function is to start a machine safely, for example, an enable pendant. This instruction energizes its output (O1) only if the Enable input is ON (1), and both safety inputs, Channel A and Channel B, transition to the active state within the Discrepancy Time.
Available Languages
Ladder Diagram
Function Block
This instruction is not available in function block.
Structured Text
This instruction is not available in structured text.
Operands
IMPORTANT:
Unexpected operation may occur if:
- Output tag operands are overwritten.
- Members of a structure operand are overwritten.
- Structure operands are shared by multiple instructions.
IMPORTANT:
Make sure safety input points are configured as single, not Equivalent or Complementary. These instructions provide all dual channel functionality necessary for PLd (Cat. 3) or Ple (Cat. 4) safety functions.
IMPORTANT:
If changing instruction operands while in Run mode, accept the pending edits and cycle the controller mode from Program to Run for the changes to take effect.
WARNING:
ATTENTION:
If changing instruction operands while in Run mode, accept the pending edits and cycle the controller mode from Program to Run for the changes to take effect. The following table provides the operand used to configure the instruction. This operand cannot be changed at runtime.
Operand | Data Type | Format | Description |
|---|---|---|---|
DCSRT | DCI_START | Tag | DCSRT structure |
Safety Function | DINT | list item | This operand provides a text name for how this instruction is being used. Choices include enable pendant (20), start button (21), and user-defined (100). This operand does not affect instruction behavior. It is for information/documentation purposes only. |
Input Type | DINT | list item | This operand selects input channel behavior. Equivalent - Active High (0) : Inputs are in the active state when Channel A and Channel B inputs are 1.Complementary (2) : Inputs are in the active state when Channel A is 1 and Channel B is 0. |
Discrepancy Time (ms) | DINT | immediate | The amount of time that the inputs can be in an inconsistent state before an instruction fault is generated. The inconsistent state depends on the Input Type. Equivalent: Inconsistent state is when either is true: Channel A = 0 and Channel B =1 Channel A =1 and Channel B =0 Complementary: Inconsistent state is when either is true: Channel A = 0 and Channel B =0r Channel A =1 and Channel B =1 The valid range is 5...3000 ms. |
The following table explains instruction inputs. The inputs may be field device signals from input devices or derived from user logic.
Operand | Data Type | Format | Description |
Enable | BOOL | tag | This input enables or disables the instruction. ON (1): The instruction is enabled. Output 1 is energized when Channel A and Channel B transition to the active state within the Discrepancy Time.
OFF (0): The instruction is disabled. Output 1 is not energized. |
Channel A 1 | BOOL | tag | This input is one of the two safety inputs to the instruction. |
Channel B 1 | BOOL | tag | This input is one of the two safety inputs to the instruction. |
Input Status | BOOL | immediate tag | If instruction inputs are from a safety I/O module, this is the status from the I/O module (Connection Status or Combined Status). If instruction inputs are derived from internal logic, it is the application programmer’s responsibility to determine the conditions. ON (1): The inputs to this instruction are valid.
OFF (0): The inputs to this instruction are invalid. |
Reset 2 | BOOL | tag | This input clears the instruction faults provided the fault condition is not present. OFF (0) -> ON (1): The FP (Fault Present) and Fault Code outputs are reset. |
1
If the input is from a Guard I/O
input module, make sure that the input is configured as single, not Equivalent or Complementary. 2
ISO 13849-1 stipulates instruction reset functions must occur on falling edge signals. To comply with ISO 13849-1 requirements, add this logic immediately before this instruction. Rename the Reset_Signal tag in this example to the reset signal tag name. Then use the OSF instruction Output Bit tag as the reset source of the instruction.
The following table explains instruction outputs. The outputs can be used to drive external tags (safety output modules) or internal tags for use in other logic routines.
Operand | Data Type | Description |
Output 1 (01) | BOOL | This output is energized when the input conditions have been satisfied. The output becomes de-energized when:
|
Fault Present (FP) | BOOL | ON (1): A fault is present in the instruction.
OFF (0): This instruction is operating normally. |
Fault Code | DINT | This output indicates the type of fault that occurred. See the Fault Codes section for a list of fault codes. This operand is not safety-related. |
Diagnostic Code | DINT | This output indicates the diagnostic status of the instruction. See the Diagnostic Codes section below for a list of diagnostic codes. This operand is not safety-related. |
IMPORTANT:
Do not write to any instruction output tag under any circumstances.
Affects Math Status Flags
No
Major/Minor Faults
None specific to this instruction. See Index Through Arrays for array-indexing faults.
Execution
Condition/State | Action Taken |
|---|---|
Prescan | Same as Rung-condition-in is false. |
Rung-condition-in is false | The .O1 and .FP are cleared to false. |
Rung-condition-in is true | The instruction executes as described in the Normal operation section. |
Postscan | Same as Rung-condition-in is false. |
Operation
Normal
The timing diagram illustrates the normal operation for a start device, for example, an enable pendant. At (A), Output 1 is not energized because the Enable input is OFF (0). At (B), Output 1 is not energized because the transition of the Enable signal ON (1) can never enable Output 1. At (C), Output 1 is energized 50 ms after the safety inputs transition through the safe state and to the active state with the Enable input ON (1). At (D), Output 1 is de-energized when either one of the safety inputs transition to the safe state. At (E), Output 1 is energized 50 ms after the safety inputs return to the active state. At (F), Output 1 is de-energized because the Enable input has transitioned to OFF (0).
Normal (Equivalent Inputs)
This diagram demonstrates the same behavior as in the previous timing diagram except that the Input Type is Complementary.
Normal (Complementary Inputs)
Input Status Fault Operation
The timing diagram illustrates fault behavior when the Input Status becomes invalid. At (A), Output 1 is not energized because the Input Status has not become active for the first time. At (B), with the Input Status active, and after a 50 ms delay, Output 1 is energized because the safety inputs have transitioned through the safe state to the active state. At (C), the Input Status becomes invalid, which immediately de-energizes Output 1 and generates a fault. At (D), the fault cannot be reset because the Input Status is still inactive. At (E), the fault is reset because the Input Status is now active and a reset is triggered. At (F), Output 1 is active.
Discrepancy Fault Operation
The timing diagram illustrates a discrepancy fault occurring when Channel A and Channel B are in an inconsistent state for longer than the Discrepancy Time configuration operand. At (A), a fault is generated when the safety inputs are in an inconsistent state for longer than the Discrepancy Time, for example, 250 ms. At (B), the fault is cleared because both safety inputs are inactive and the reset went active. At (C), Output 1 is energized 50 ms after both safety inputs transition to the active state together within the Discrepancy Time. At (D), Output 1 is de-energized when Channel B transitions to the safe state. At (E), a fault is generated because the safety inputs are again in an inconsistent state for longer than the Discrepancy Time. At (F), the fault is cleared, but Output 1 is not energized until both safety inputs transition to the active state together.
False Rung State Behavior
When the instruction is executed on a false rung, all instruction outputs are de-energized.
Fault Codes and Corrective Alarms
The fault codes are listed in hexadecimal format followed by decimal format.
Fault Code | Description | Corrective Action |
0 | No fault. | None. |
16#20 32 | The Input Status input transitioned from ON (1) to OFF (0) while the instruction was executing. |
|
16#4000 16384 | Channel A and Channel B were in an inconsistent state for longer than the Discrepancy Time. At the time of the fault, Channel A was in the active state. Channel B was in the safe state. |
|
16#4001 16385 | Channel A and Channel B were in an inconsistent state for longer than the Discrepancy Time. At the time of the fault, Channel A was in the safe state. Channel B was in the active state. | |
16#4002 16386 | Channel A went to the safe state and back to the active state while Channel B remained active. | |
16#4003 16387 | Channel B went to the safe state and back to the active state while Channel A remained active. |
Diagnostic Codes and Corrective Actions
The fault codes are listed in hexadecimal format followed by decimal format.
Diagnostic Code | Description | Corrective Action |
0 | No fault. | None. |
16#20 32 | The Input Status was OFF(0) when the instruction started. | Check the I/O module connection or the internal logic used to source input status. |
16#4000 16384 | The device is not in a safe state at start-up. | Release the start device (put Channel A and Channel B in a safe state). |
16#4060 16480 | The device is not enabled. | Enable the device (set Enable to 1). |
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