Curtis PMC 1297 Manual
49
The 1297 controls the operation of the load-hold valve and the proportional lowering
valve, as shown in Figure 21. By so doing, it controls the hydraulic path for Lift and
Lower operations. Some hydraulic systems have a proportional lowering valve but no
load-hold valve. Others have a simple open/closed lowering valve in place of a
proportional valve. In these systems, variable lowering (i.e., lowering in proportion
to the amount of throttle applied) is not possible. See box at the bottom of the next
page for more information about this kind of system.
LV MAX CURR
The Lower speed is determined by the aperture of the lowering valve. The LV
maximum current parameter sets the maximum current the controller will
provide to the lowering valve. The LV maximum current is programmable from
0.0 to 3.0 amps.
For proportional valves, the LV maximum current can be set to limit the
valve’s full aperture. Non-proportional valves always open completely; for these
valves, the LV maximum current should be set to the valve’s full current rating.
LV MIN CURR
The LV minimum current parameter sets the minimum current through the
lowering valve. Most proportional valves need a non-zero closed current in order
to start opening immediately when Lower is requested. The LV minimum
current is programmable from 0.0 to 1.0 amp. For non-proportional lowering
valves, the controller does not look at this parameter so its setting is irrelevant.
LV DITHER
The lowering valve dither feature provides a constantly changing current in the
coil to produce a rapid back-and-forth motion of the valve. This keeps propor-
tional valves lubricated and allows low-friction, precise movement. The LV
dither % parameter specifies the amount of dither as a percentage of the LV
maximum current, and is applied in a continuous 200 Hz cycle of none–add%–
none–subtract%. The LV dither is programmable from 0 to 100%.
For non-proportional lowering valves, where the valve’s opening and
closing is spring-activated, dither is not applicable. If your application uses this
type of lowering valve, set the dither parameter to 0%.
LV ACCEL
The LV current acceleration rate parameter specifies how long it will take the
lowering valve current to increase from 0% to 100%. The LV current accel rate
is programmable from 0.0 to 3.0 seconds.
Valve Control Parameters
3
B
— PROGRAMMABLE HYDRAULIC PARAMETERS: Valve Control
To Next Page
Loading...
Need help?
General
