Application Note

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. [phone] or
Fax [phone]
In Europe/M-East/Africa (31 40) 2 675 200 or
Fax [phone]
In Canada (800)-36-FLUKE or
Fax [phone]
From other countries [phone] or
Fax [phone]
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
789’s 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 it’s 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.