|
Frequently
Asked Questions
All
Modules - Control Pressures
Q:
How do the control valves in
Scanivalve Modules operate? Answer
Q:
What are control pressures? Answer
Q:
How do the control pressures operate the
valves? Answer
Q:
Do control pressures have to be applied
at all times? Answer
Q:
Is it possible to minimize the
number of control pressures needed? Answer
Q:
What quality of air should be
used for control pressures? Answer
How
do the control valves in Scanivalve Modules operate?
All, ZOC16TC, ZOC17, and DSA modules have four
way valves for each sensor. Application of a control
pressure causes a piston in each valve to compress
an o-ring, forming an air tight seal. All of these
valves are capable of, and have been tested to,
a minimum of one million operations.
All ZOC 22, 23 and 33 modules also have four way
valves for each sensor. These valves use inflatable
bladders instead of pistons. Although the method
is somewhat different, the bladders are able to
form air tight seals.
Read
FAQs on control pressures
View
all FAQ topics
What
are control pressures?
Control pressures are used to switch the valves
in a module to one of the standard operating modes:
Zero, Operate, Calibrate, and Isolate. Electronic
signals are not required to switch these valves.
Read
FAQs on control pressures
View
all FAQ topics
How
do the control pressures operate the valves?
Each module requires two or three control pressures
to operate the valves, depending on the valve
logic. ZOC16TC, ZOC17 and all DSA modules require
three pressures. Two of the pressures control
the normal valve modes. The third pressure controls
a separate purge valve.
ZOC22,
ZOC23, and ZOC33 modules also require two or three
control pressures. The standard versions of these
modules require two control pressures. The Duplex
versions of these modules require a third control
pressure to operate the Duplex valve.
The different modes of operation are obtained
by applying the control pressures in a logical
sequence. Truth Tables may be found in the appropriate
module hardware manual that show the logic required
for proper operation.
Read
FAQs on control pressures
View
all FAQ topics
Do
control pressures have to be applied at all times?
All DSA series, ZOC16TC, and ZOC17 modules are
normally open valves. That is, no control pressure
is required to put the module in the Operate mode.
Control pressures are required to switch the valves
to the other modes of operation. The control pressure
used for these modules must be 85 to 105 psi depending
on the pressure range of the module.
All
ZOC22, ZOC23, and ZOC33 modules require a control
pressure for each mode of operation. The control
pressure for these modules must be 60 to 65 psi.
Read
FAQs on control pressures
View
all FAQ topics
Is
it possible to minimize the number of control
pressures needed?
In some cases, yes. For DSA modules, a single
control pressure may be used for Zero Calibrations.
Also, Ctl 1 and Ctl 2 may be applied from the
same source to switch the module into the Calibration
mode. ZOC22, 23, and 33 modules must have all
control pressures available.
Read
FAQs on control pressures
View
all FAQ topics
What
quality of air should be used for control pressures?
In order to prevent damage to the valves and sensors,
the control pressures for all modules must be
Instrument Grade. For more information, please
refer to ISA Specification ISA-S7-3.
Read
FAQs on control pressures
View
all FAQ topics
|
