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equipment if allowed to continue.
DC
Direct Current. Such as a battery. The voltage is stable, and does not
oscillate (at least intentionally).
Digital
A simple ON/OFF condition. For example, the presence or lack of a 120VAC
signal on a wire is a digital condition.
DSR
Downstream Relief Valve is used to limit the maximum allowable downstream
pressure.
Equal HP pumps
Also referred to as interchangeable pumps. Defines which pumps are
available to start based on lowest run time. VSPs and XL pumps are defined
in the PLC program. An XL pump can be an equal HP pump, but it will not
start as a lead pump, because the lead pump will always be a VSP.
Filter
A device used downstream of the pumps to clean the water being pumped
into the irrigation. These devices are typically self-cleaning, but require
hardware/software to self-clean.
Fixed speed
Pumps run at a fixed RPM, defined by the motor windings and the frequency
of the line voltage (50/60 Hz).
Flooded suction
A type of system where the pumps (usually centrifugal) are fed by a pond or
other body of water at very low pressure (atmosphere, or just a few feet of
water column). Pumps for these systems must be carefully selected for low
NPSHR (Net Positive Suction Head Requirements) or cavitation and pump
damage can occur. Low inlet pressure safety is an excellent choice for these
systems.
Foot valve
A device used primarily on horizontal lift applications to maintain pump prime.
Frequency
(Hz) The number of oscillations per second of any system. Typically used to
refer to electrical systems, such as AC power line frequency, or variable
speed drive output frequency. This frequency defines the speed of an AC
motor.
GPM
Gallons per minute. Units of flow for US use.
HSS
High speed switching. Starting pumps with a VFD to reduce inrush current
and provide pressure control, but able to switch over to fixed speed so that
the VFD is able to start another pump.
Input
A way for a control system to detect real-world occurrences. These can be
digital or analog.
Inverter
Another term for Variable Frequency Drive (VFD). Actually, more correctly
applied to the output circuitry of the drive, which converts DC voltage to AC
voltage.
Lag pump
A pump used later in the pump sequence to support increasing irrigation
demand requirements. The term lag simply refers to the fact that it does not
start first.
Lake fill
(LLC) A circuit designed to keep a pond or lake at or above some minimum
level of water.
Lead groups
Proprietary term used to describe the register(s) that defines which pumps on
a station are interchangeable in their pressure/flow characteristics.
Lead pump
The pump in a lead group which is chosen by the controller to start first. This
is usually determined by finding the pump in the lead group with the lowest
