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In-field valve positioner checks using the Fluke 789 ProcessMeter Application Note
Valves, the actuators that move
them, and the electronic circuits
that control them, are all subject
to the effects of aging soon after
they are installed. The valve seat
wears not only from the repeated
seating of the valve, but from the
liquid or gas that passes through
it. Depending on the application,
a valve can be stroked from hun-
dreds to tens of thousands of
times over a one-year period.
This amount of mechanical
motion inevitably causes screws
to reposition, springs to weaken
and mechanical linkage to
loosen. In addition, electronic
components change value over
time. The results are valves that
dont fully open or close, close
prematurely, or operate erratically
and cause improper regulation of
General steps in checking
valve positioning.
The first order of business is to
set up the ProcessMeter in the
sourcing mode using the appro-
priate range of current for the
positioner. The Fluke 789 uses a
separate pair of jacks to source
current. First connect the test
leads into the 24 V loop power
mA output jacks. Next, select the
4-20 mA range by moving the
function switch from Off to the
first mA output
position. Now
youre ready to connect the 789
to the input terminals of the valve
positioner.
With the test equipment prop-
erly set up and connected to the
positioner, its time to determine
if the positioner fully closes the
valve at the 4 mA input current
level. Using the push buttons on
the ProcessMeter, adjust the
source current to 4.0 mA. Now,
while watching the valve for any
movement, press the Coarse
Down button once to decrease
the current to 3.9 mA. There
should be no movement of the
valve. In setting the point at
which the valve starts to open,
you want to be sure there is no
counter pressure by the actuator
against the force holding the
valve closed when there is
4.0 mA on the controllers input.
In a spring-to-close valve, there
should be no pressure on the
diaphram. With a double acting
piston actuator, there should be
no pressure on one side of the
piston. You may want to set the
start of opening between 4.1 and
4.2 mA to get that insurance at
the closed setting. To check the
opening of the valve, press the
Coarse button up from 4.0 mA.
The ProcessMeter will increase
0.1 mA for each press of the
Coarse button. You should adjust
the zero adjustment on the posi-
In-field valve positioner
checks using the
Fluke 789 ProcessMeter F r o m t h e F l u k e D i g i t a l L i b r a r y @ w w w . f l u k e . c o m / l i b r a r y
the gas or liquid under its control.
This is more commonly referred
to as calibration drift.
To keep a system operating
properly, a good preventative
maintenance program that man-
dates periodic checks of valve
positoners is required. These
checks need to be conducted
quickly to minimize down time.
When these checks reveal cali-
bration drift, recalibration of the
electronic valve positioner must
be performed quickly. With the
varied locations in which a valve
can be installed and the difficulty
in removing it, the equipment
used to perform the checks must
be brought to the valve positioner
itself. Therefore, this in-field
tester must be portable, easy to
use and rugged. Flukes 789
ProcessMeter is a perfect
solution.
With its signal sourcing capa-
bility, the Fluke 789 can simulate
a controller connected to a valve
positioners input. Through the
controls on the ProcessMeter, you
can set the positioners input
current to a specified level and
visually inspect the reaction of
the valves position using the
mechanical position indicator, the
valve stem position or flow indi-
cators. In addition, the Fluke 789
can continuously adjust the
source current in a ramping or
stepping fashion, allowing you to
check the valves linearity and
response time.
An example will help explain
how simple it is to use a Fluke
789 ProcessMeter for these
checks. This example only
demonstrates the basic principles
in making position checks on a
valve positioner. Manufacturers
specific instructions should
always be consulted for proper
and appropriate valve positioner
testing and calibration. Fluke. Keeping your world
up and running.
Fluke Corporation
PO Box 9090, Everett, WA USA 98206
Fluke Europe B.V.
PO Box 1186, 5602 BD
Eindhoven, The Netherlands
For more information call:
In the U.S.A. (800) 443-5853 or
Fax (425) 446-5116
In Europe/M-East/Africa (31 40) 2 675 200 or
Fax (31 40) 2 675 222
In Canada (800)-36-FLUKE or
Fax (905) 890-6866
From other countries +1 (425) 446-5500 or
Fax +1 (425) 446-5116
Web access: http://www.fluke.com/
�2002 Fluke Corporation. All rights reserved.
Printed in U.S.A. 9/2002 2041342 A-ENG-N Rev A
tioner to set the valve for the
closing you desire.
The next check is with the
valve at the next extreme: fully
open. This is referred to as a span
position check. Using the range
buttons on the ProcessMeter,
adjust the source current for a
20 mA reading and allow time
for the valve to stabilize. While
watching or feeling for valve
movement, press the Coarse Up
range button once to 20.1 mA.
This movement should be as small
as possible and can be adjusted
using the span adjustment on the
positioner. Using the coarse con-
trol of the 789, adjust current up
and down between 20.1 mA and
19.9 mA. There should be no
movement of the valve stem from
20.1 to 20 mA and slight move-
ment from 20 mA and 19.9 mA.
In most valves, there is an
interaction between the zero and
span settings of a valve controller.
Therefore, it is best to ensure
proper valve position adjustment
by repeating the test of the fully
closed and fully open positions
until no further adjustment is
necessary.
For valves with linear action,
linearity can be checked by set-
ting the Fluke 789 to 4 mA and
then, using the % Step button,
step the current to 12 mA (50 %)
and confirm the valve position
indicator is at 50 % travel. If your
valve is of a non-linear type,
refer to the valve manual for
proper operation.
Checking for smooth valve
operation is easy with the Fluke
789s Slow Ramp function. Set
the rotary switch to output mA
and select Slow Ramp using
the blue button. Allow the 789 to
ramp through several cycles
while watching or feeling for any
abnormal operation of the valve.
The valve should NOT oscillate or
hunt at any of the step positions
of the Slow Ramp. At the same
time however, the valve should
not be sluggish. You set the gain
of the valve controller to a point
that gives the best response
between these two conditions.
As the example above shows,
the Fluke 789 ProcessMeter
brings all the necessary tools to
the job site for checking and
recalibrating electronic valve
positioners. In addition, the
Fluke 789 not only simulates a
current loop transmitter, but its a
measurement tool as well. Along
with the normal DMM measure-
ments (dc/ac volts, dc/ac current,
and resistance), the 789 can also
measure frequency. Additional
features include MIN\MAX,
Relative measurements, Diode
Test and AutoHold. A feature-rich
product designed specifically for
the loop process technician,
the Fluke 789 ProcessMeter
also complies with IEC 1010-1
standard for CAT III 1000 V
environments. Contact your local
Fluke distributor for pricing and
availability.
Safety note:
Always ensure that the personnel responsi-
ble for the process you are working on are
informed of your intentions prior to making
any checks of valve operation. Be alert when
touching any moving machinery.