West Control Solutions 8700+ - Manual (Page 163)

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- DIN Controllers & Indicators - Product Manual
Page 158
Glossary 59305, Issue 7 – March 2014
Valve Close Limit Type: VMD Controller Parameter
When Valve Position Indication is to be used on Valve Motor Controllers, this parameter
provides a “clamp” on the upper valve position, which the controller will not attempt to drive
the valve past. It can be set between

(fully closed) and the Valve Open Limit value –1,
expressed as a percentage of the valve’s “fully open” position.
The Auxiliary Input must correctly scaled using the Set Valve Open and Closed parameters
before using this parameter.
Display code =

, default setting =

.
Also refer to Auxiliary Input, Set Valve Closed Position, Set Valve Open Position, Valve Open
Limit, Valve Motor Control and Valve Position Indication.
Valve Motor Drive Control Type: VMD Controller Definition
Valve Motor Drive Controllers are designed to control Modulating Valves using a special
“Open Loop” Valve Motor Drive (VMD) PI control algorithm. Output signals are provided to
move the valve further open, or further closed when the process is higher or lower than the
desired setpoint. When on setpoint, no output is required to maintain control unless load
conditions change. This known as Three-Point Stepping control.
Valve Position or Flow Indication is possible if an Auxiliary Input option module has been
fitted and configured for this purpose.
Also refer to Auxiliary Input, Modulating Valve, Open Loop VMD, PI Control, PID, Setpoint
and Valve Position Indication.
Valve Position or Flow Indication Type: VMD Controller Definition
The Valve Motor Drive Controllers do not require any kind of position feedback in order for
the PID algorithm to correctly control the process. However, where feedback or flow level
signals are available, they can be displayed as a percentage (

to

) of the possible valve
opening or flow level. Valve Position Indication is shown in the Operator Mode lower display
in place of the Setpoint when the Display Strategy is set to

.
Valve Position Feedback is usually provided by means of a potentiometer linked to the valve.
Potentiometers can be directly connected to the Full Auxiliary Input (Option Slot B only).
Flow meters typically have linear 0-20/4-20mA or 0-5/0-10V signals, which can be used with
either the Full Auxiliary Input or the Basic Auxiliary Input (Option Slot A only) of the
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VMD Controllers.
Even when position feedback is provided in this way, the information is not used by the Open
Loop VMD control algorithm when positioning the valve, avoiding problems associated with
faulty feedback signals.
Also refer to Auxiliary Input, Display Strategy, Open Loop VMD, PID, Set Valve Closed
Position, Set Valve Open Position, Setpoint, and Valve Motor Control.
Valve Open Limit Type: VMD Controller Parameter
When Valve Position Indication is to be used on Valve Motor Controllers, this parameter
provides a “clamp” on the upper valve position, which the controller will not attempt to drive
the valve past. It can be set between

(fully open) and the Valve Closed Limit value +1,
expresse d as a percentage of the valve’s “fully open” position.
The Auxiliary Input must correctly scaled using the Set Valve Open and Closed parameters
before using this parameter.
Display code =

, default setting =

.
Also refer to Auxiliary Input, Set Valve Closed Position, Set Valve Open Position, Valve
Close Limit, Valve Motor Control and Valve Position Indication.