Emerson Rosemount 56 - Bleed and Feed

Section 9: Alarm Relay Functions Instruction Manual
April 2017 LIQ-MAN-56
70 Alarm Relay Functions
*
See Appendix 1 – HART and Device Variables
9.4 Bleed and Feed
9.4.1 Description:
A bleed and feed timer is typically used to replace chemicals lost during blowdown. It
involves two or more relays. The bleed relay is a normal setpoint alarm relay. Once the bleed
relay deactivates, one or more feed relays activate for a percentage of the time the bleed
relay was on.
Bleed and Feed supports continuous monitoring of blow-down water conductivity to
determine the point of excessive conductivity. At a programmable maximum concentration
value, dumping (bleeding) of the excessively dirty blow-down water is triggered.
Subsequently, pumping (feeding) of additional make-up water chemicals is enabled to
account for lost blow-down water. Through level control, make-up water is added in
proportion to the volume of blowdown material lost through dumping and evaporation.
A schematic of the Bleed and Feed timer operation is shown:
9.4.2 Setup
Access Bleed and Feed Timers by pressing ENTER/MENU from the main screen and then
Program/Relays/Configure Relay. From the main relay programming screen, program this
feature as follows:
1. Relay: Assign relay 1 for Bleed and Feed and press ENTER/MENU.
2. Type: Select Bleed and Feed as the relay type and press ENTER/MENU.
3. Assign: Assign S1 (sensor 1), S2 (sensor 2 if available) or other available parameters to
the designated relay and press ENTER/MENU.
4. Logic: Set High for high setpoint or Low for low setpoint and press ENTER/MENU.
Relay Function Limits and Selections Default
Delay Timer NA NA
Logic Low/High High
Setpoint * *
Deadband * 0.000
Normal state Close/Open Open
T
able 9-3. Defaults and programmable limits
Figure 9-3. Bleed and feed timer alarm operation
time
bleed on
on
off
AL1
(bleed)
AL2
(feed)
feed on
delay
feed time = X% of bleed time