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Poll Cycle Settings
A Poll Cycle is the set of request messages read and/or write messages for a given device that are transmitted and processed for a device when a schedule comes due, or a when a non-scheduled event occurs (such as a demand poll or history collection request).when:
- A schedule comes due
- A demand poll is performed
- The "Retrieve History" command is manually executed
Poll Retries
- Default = 2. The number of times a Poll Cycle
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- can be attempted.
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- It applies to scheduled and non-scheduled Poll Cycles.
- If a valid response is received for all
- messages
- in the Poll Cycle, it is considered complete.
- ACM will then move on to the next device handled by that port.
- If
- one or more messages has the state "No Response" and the number of poll retries has not been reached, the Poll Cycle is considered incomplete
- and is placed into
- the retry queue
- for that port.
- If all Poll Cycle Retries are incomplete, the Poll Cycle is considered failed and the message "{Device Name} no more retry delays" will appear in the logger.
Fail Delay
- Default = 30. The Fail Delay is
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- used to
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- lengthen the minimum period of time that must elapse between Poll Retries
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- . It applies to scheduled Poll Cycles only
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- .
- If there are many incomplete Poll Cycles
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- for the port, the retry queue may grow causing the time period between Poll Retries to lengthen.
- Note: Incomplete Poll Cycles for non-scheduled events will be processed
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- when they reach the front of the queue, whether the Fail Delay time has elapsed or not.
Poll Message Settings
A poll message is a single request, or transmit, to a field device. Gathering data from a field device typically requires multiple poll messagesread or write message.
Message Retries
- Default = 2. The number of times a single message
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- can be sent.
- If a valid response is received, the
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- next message in the Poll Cycle will be sent.
- If a valid response is not received and the number of message retries has not been reached, the message will be
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- sent again
- If a valid response is
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- never received
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- for the message
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- , the
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- message state will be set to "No Response" and ACM will move to the next message in the cycle unless "Abort Poll After First No Response" is checked in which case the Poll Cycle is considered "incomplete".
Reply Timeout (in milliseconds)
- Default = 2000
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- . This is the length of time ACM will wait for the
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- entire response to be received before setting the message state to "Incomplete" if there are retries left, or to "No Response" if not. I.e. After a message is sent, there are X number of milliseconds that may pass without a complete response before ACM considers the message failed.
Initial Timeout (in milliseconds)
- Default = 0 (
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- disabled).
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- This is the length of time
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- ACM will wait for the first
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- byte of
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Inter-Character Timeout
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- the response to be received before setting the message state to "Incomplete" if there are retries left, or to "No Response" if not. I.e. After a message is sent, there are X number of milliseconds that may pass without any response before the ACM considers the message failed. If this setting is 0, no initial timeout is applied.
Inter-Character Timeout (in milliseconds)
- Default = 0 (disabled). This is the length of time ACM will wait between bytes before considering setting the message state to "Incomplete" if there are retries left, or to "No Response" if not. I.e. When a byte is received, there are X number of milliseconds that may pass without receiving any more bytes before the ACM considers the message failed. If this setting is 0, no inter-character timeout is applied.
- Common usage: This property is useful with a slow connection where only a few bytes of data are received at a time. In that scenario, the Reply Timeout given a lengthier time period to ensure the port waits for the full response if it continues to receive data bytes. If
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- more time passes between received bytes than the value in the Inter-Character Timeout field, ACM will consider the message failed at that time instead of waiting the duration of the "Reply Timeout".
Skip Retries on Failed Devices
A "failed device" is a device for which all poll cycle retries failed.
- Default = Not selected.
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- This setting determines whether or not to attempt all poll retries for a failed device on subsequent poll cycles.
- When this option is not selected, there is no change to the "Poll Retry" behavior explained above.
- When this option is selected, ACM will only attempt the poll cycle one time, disregarding the "Poll Retry" count until the device has a successful poll.
Common Usage: This property is useful to prevent extra polls when devices are known to be offline
Warning Enabling this option for devices on poor communication links may result in failure to collect data
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.
Abort Poll After First No-Response
Default = Not selected. When all configured Message Retries have been transmitted and no valid response has been received, a message is in a No-Response state. If this occurs, and the option to ‘Abort Poll After First No-Response’ is enabled, then no more request messages will be transmitted for the device during its current poll cycle. Polling for this device will continue the next time its schedule comes due, or if a non-scheduled event occurs (such as a demand poll)This option applies to how the Poll Cycle processes message if a single message's state is setting the message status to "No Response". Without this selected, a Poll Cycle will continue to process all messages in the cycle, ignoring message states. When it is selected, no more messages in the Poll Cycle will be sent after a single message with state "No Response" and will be considered "incomplete".
Dialup Modem Tab
Command Retries.
The maximum number of tries to issue a modem command with no response before continuing to another poll. Default = 2.
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