Signet 9900 Operating Instructions Manual page 22

Relay Outputs
100%
80%
60%
40%
20%
0%
Relay is PWM
Minimum
always OFF
22 9900 Transmitter
PWM
Maximum
Range
Relay is
always ON
Process value
• Pulse Width Modulation
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 9900 must be programmed with the relay period, and with
the low and high setpoints.
NOTE: The PWM mode is not used for Pressure applications.
NOTE: Relay LEDs are not lit in PWM mode.
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.
• Volumetric Pulse
A pulse is generated each time a specifi ed volume of fl uid is
registered. For fl ow inputs only.
NOTE: Relay LEDs are not lit in VOLUMETRIC PULSE mode.
• Totalizer Volume
Relay activates and latches when a specifi ed volume of fl uid is
registered. For Flow inputs only.
Total Volume mode counts the TOTALIZER Units until the
setpoint volume is reached, then turns on the relay until the
resettable totalizer is reset.
If the Resettable Totalizer reading is greater than the setpoint,
the relay will be turned on immediately. The relay will be off
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 fi lter change.