F
OR
M
ODELS
: JGI, JGM, JGN, JGP
AND
JGQ
S
ECTION
4 L
UBRICATION
PAGE 4-23
Divider block monitoring devices define their operation opposite from other industries.
Most other industries define the switch state as the state the switch is in when it is on the
shelf. (That is: If a momentary push button switch is NO, then when it is taken out of the
box the switch will be open until the button is pushed and the contact will close. If a
momentary push button switch is NC then when it is taken out of the box the switch will
be closed until the button is pushed.) This does not apply to divider block monitoring
devices.
Divider block device manufacturers have "simplified" things for the mechanic. Normally
Open (NO) refers to the state the switch is in when the divider block is cycling or the unit
is running. An NO switch means that when the unit is running the shutdown switch is
open or non-failsafe. If a wire falls off or is cut while the unit is running the control system
will never stop the unit. If the device is damaged or a wire has come loose at startup the
control system would never know there is a problem. An NC switch means that when the
unit is running the shutdown switch is closed or failsafe. Now if a wire falls off or is cut the
control system will detect that the switch is open and shutdown the unit.
Ariel recommends using a NC (failsafe) switch. However, when a NO (non-failsafe)
switch is used, Ariel recommends testing the shutdown circuits at least once a month.
II. Proximity switch
- This is a device that will sense the position of the divider block piston
and will produce a switch change of state or a pulse every time the pin changes position.
This device must be combined with a PLC or some other counter/timer device to produce
the shutdown. Some devices on the market will open the switch when the pin is toward the
left and close when the pin is toward the right. Others will produce a 0.5 second pulse when
the pin moves from left to right. If this is used it is the responsibility of the control system to
sense the switch cycling and stop the unit if a block stops cycling.
APPLICATION NOTES
- Proximity Switch
Ariel recommends setting up the control system to find the time between cycles triggered
when the switch transitions from off to on. See Figure 4-7 suggested control system
block diagram.
1.
Shutdown time with no lubrication - The distribution block cycle times will vary
slightly from cycle to cycle. Seeing 12 seconds one cycle then 15 seconds the
next then 14 the next is normal. The recommended shutdown time is: 2 times
the design cycle time + 30 seconds limited between 30 seconds and 3 minutes.
LIMIT (2 x design cycle time + 30 seconds) 30, 180
Design cycle time is found on the compressor lube sheets or tag on the com-
pressor.
2.
DE-BOUNCE and latching circuits - Depending on the device and control sys-
tem scan time it may be necessary to include de-bounce hardware and/or soft-
ware. Some of the devices do not have built in de-bounce circuits and can cause
a fast control system to double or triple count. Other times it may be necessary
latch the input thus allowing the control system to detect only the first transition
from low to high. This becomes significant when displaying the cycle time for the
operator to set the pump flow rates and when calculating the total oil through the
divider block.
3.
Suggested Operator Displays:
