Tuning Policy Properties for N2 Networks
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Property
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Description
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Min Write Time
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Applies to writable proxy points, especially ones that have
one or more linked inputs. Specifies the minimum amount of time allowed between
writes. Provides a method to throttle rapidly changing values so that only the
last value is written. If this property value is 0 (default), this rule is
disabled. All value changes enable writes.
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Max Write Time
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Applies to writable proxy points. Specifies the maximum
wait time before rewriting the value (in case nothing
else has triggered a write). Any write action resets this timer. If property
value is 0 (default), this rule is disabled (no timed rewrites).
| Note: | Setting this to a specific value, for example 10 minutes,
may be useful. Often, a network may have devices that upon a power cycle (or
even a power bump), have writable points that reset to some preset default
value or state. Note that often in a site-wide power bump of a few seconds,
such field controllers (devices on the network) typically reset, but an FX
Supervisory Controller continues normal operation on backup battery. Since the
network’s default monitor ping is usually 5 minutes, the station (network) may
never mark these devices as down, such that a Write On Up does not occur. If a
writable point represents an AHU or chiller that defaults to unoccupied
following a device reset, the load never restarts until the next day, when the
schedule toggles. You can correct this issue by assigning the point to a tuning
policy that does have a configured Max Write Time. At the same time, realize
that many networks may be configured such that multiple masters may be issuing
conflicting writes to one or more points in a device. Exercise caution with
this property in this case, to avoid write contention that could result in
toggling loads.
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Write on Start
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Applies to writable proxy points. Determines behavior at
station startup.
If set to
true (default), a write occurs when the station first
reaches steady state.
If set to
false, a write does not occur when the station reaches
steady state.
| Note: | Consider setting this property to
false in most tuning policies, except for tuning
policies selectively assigned to more critical writable proxy points. This is
particularly important for large networks with many writable proxy points.
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Write on Up
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Applies to writable proxy points. Determines behavior when a
proxy point (and parent device) transitions from down to up.
If set to
true (default), a write occurs when the parent device
transitions from down to up.
If set to
false, a write does not occur when the parent device
transitions from down to up.
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Write on Enabled
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Applies to writable proxy points. Determines behavior when a
proxy point’s status transitions from disabled to normal (enabled).
If set to
true (default), a write occurs when writable point
transitions from disabled.
If set to
false, a write does not occur when writable point
transitions from disabled.
| Note: | The disabled-to-enabled status transition can be
inherited globally by points if the parent device had been set to disabled or
network-wide if the driver network was set to disabled. Therefore, be aware
that if left at true in tuning policies, that all associated writable points
receive a write upon either the device or network when it transitions from
status disabled to enabled.
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Start Time
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If set to a non-zero value, points become stale (status stale)
if the configured time elapses without a successful read, indicated by Read
Status ok.
If set to
zero (default), the stale timer is disabled, and points
become stale immediately when unsubscribed.
By default, proxy point status stale is indicated by tan
background color. In addition, stale status is considered invalid for any
downstream-linked control logic.
| Note: | We recommend that you specify the stale time to be at
least three times the expected poll cycle time. Most peer-to-peer networks do
experience collisions and missed messages. You may see nuisance stale statuses
if you set the stale time too short. If a message is missed for some reason,
then another poll cycle time or two is allowed for the message to be received
before setting the stale flag.
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