Low
• Relay is activated when the process variable is less than the setpoint.
• The relay is deactivated when the process variable becomes greater than the sum of the setpoint and the
hysteresis.
Product(s)
2551
5075
5500
5700
5800
8250
8350
8450
8550
8750
8850
8860
8900
High
• Relay is activated when process variable is greater than the setpoint.
• The relay is deactivated when the process variable becomes less than the sum of the setpoint and
the hysteresis.
Product(s)
2551
5075
5500
5700
5800
8250
8350
8450
8550
8750
8850
8860
8900
Window
• In Window mode, a single relay is activated when the process variable moves above
or below a fixed window of
values.
• The relay is deactivated when the process variable moves inside the window by
more than the hysteresis value.
Product(s)
8900
Proportional Pulse
• Proportional Pulse mode varies the frequency of pulses in direct
proportion to minimum and
maximum setpoints.
• The 8900 does not allow use of this mode for Pressure applications.
• Example:
• The output will be 0 pulses/min. at process values less than 5.0.
• The output will be 50 pulses/min. when the process value is 7.5.
• The output will be 100 pulses/min. at process values above 10.
Product(s)
2551
8250
8350
8750
8850
8860
8900
Pulse Width Modulation (PWM)
• PWM automatically varies the ratio of ON time to OFF time
proportional to minimum and maximum range settings.
• The relay period is the sum of the time a relay is ON and the
time it is OFF.
• Relay pulse width is the time the relay is ON.
• The 8900 must be programmed with the relay period, and with
the low and high setpoints.
• The 8900 does not allow use of this mode for Pressure
applications.
• Example:
• The pulse width will be 0% of the relay period (relay always OFF)
when the process value is less than the
minimum range.
• The pulse width will be 100% of the relay period (relay always
ON) when the process value is greater than the
maximum range.
• The pulse width will be 60% of the relay period when the process
value is at 60% of the span between the
minimum and maximum
range.
Product(s)
8900
Volumetric Pulse
• A pulse is generated each time a specified volume of fluid is
registered. For flow inputs only.
Product(s)
5075
5500
8550
8900
Totalizer Volume
• Relay activates and latches when a specified volume of fluid
is registered. For flow inputs only.
• Total Volume mode counts the TOTALIZER Units until the
setpoint volume is reached, then activates the relay until
the
resettable totalizer is reset.
• If the Resettable Totalizer reading is greater than the
setpoint, the relay will be activated immediately. The relay
will be deactivated when the totalizer is reset to zero.
• This mode is useful to trigger a reminder when a process is
due, as for a backwash cycle or filter change.
Product(s)
8900
USP
USP (United States Pharmacopoeia) has defined a set of conductivity values (limits) to be used for pharmaceutical water. The standard requires that conductivity measurement without temperature compensation be used for these applications. The limits vary according to the temperature of the sample. It will automatically determine the proper USP limit based on the measured temperature.
(This function utilizes high and low alarms based on USP values stored inside the memory of
Signet's 8860 and 8900 Instruments. )
