Emerson Rosemount 3490 Series, Reference Manual

Page: 111 / 190

D809 = (PV
now
– PV5
seconds ago
)
×
12
The On and Off points of a Rate of Change (RoC) mode relay are used as high and low
limits for read-only parameter D809. Limit values are in units of PV per minute (PV/min)
and can be in any order of value. The relay is energized while D809 exceeds the higher
limit value or falls below the lower limit value.
Typically, where the PV value is a liquid level measurement, the RoC relay can be used to
warn of a quickly rising or falling liquid level. Alternatively, the RoC mode relay can be used
for controlling the rate of liquid flow.
Related information
Pump efficiency alarm (Rosemount 3491 and 3492 only)
Pumped volume totalizing
Pump on delay
Menu
SETUP
→
[CONTROLLER]
→
OUTPUT
→
RELAY
→
OVERRIDES
Table 4-15: Pump On Delay Parameter
Parameter Description Factory default
P499 Pump On Delay This function is to prevent pumps from all being
switched on simultaneously, which could cause a
massive surge.
When multiple relays are used for pump control (or
as a set point) and power is lost, this function
provides a delay of 0 up to 9 seconds (3 seconds by
default) for the second, third, fourth, and fifth relay
when power is re-established.
3 s
Auto-sequence (Rosemount 3491 and 3492 only)
Optional automatic rotation of the leading (most used) relay can be applied to Assist or
Standby mode relays. To use these options, two or more relays must have the same mode.
The lowest numbered relay is initially the lead relay.
Note
The rotation of relays is performed without the actual swapping of values between relay
parameters.
Table 4-16: Auto-sequence Parameters
Parameter Description Factory default
P270 Auto Seq Enable Select a rotation auto-sequence. All options are
summarized in Table 4-17 .
Off
P271 Auto Seq Qual This defines the threshold (e.g. how many starts)
before applying an auto-sequence to rotate the 'lead'
to the next relay with the same mode. 0
Reference Manual Getting started
00809-0100-4841 January 2021
Emerson.com/Rosemount 111