-7-
Released 2018-01-26
Bulletin No. PAXLCL-E
Drawing No. LP0567
6.0
APPLICATIONS
Example
1:
A PAXLCL is to be calibrated to match a flow transducer whose output
is 10 mA @ 0 GPM and 50 mA @ 1375 GPM.
READOUT SPAN (Rs) = 1375 - 0 = 1375
SWING CURRENT (Is) = 50 mA - 10 mA = 40 mA
ADJUSTMENTS
(Refer
to
the
transfer
curve
below)
Null the unit to zero readout @ 0
current per Steps 1 to 4 of the
calibration steps.
Set the coarse and fine span
adjustments to get a readout of
1375 @ 40 mA per Steps 5 and 6.
Note: With the full standard swing
of 40 mA, the coarse span switch
reference markings can be used to
determine settings as follows:
S7 ON (1050) + S9 ON (260) =
1310 Span set with switches.
375 (needed) - 1310 (with SW’s)
= 65 w. fine span adj.
Set offset to readout 0 @ 10 mA per Step 7. Note: The read out
observed when the 10 mA min. current is first applied can be used to
determine the offset switch settings.) In this example the readout will
be (+) 344 when the 10 mA min. current is first applied. Applying -344
offset then reduces the readout to zero @ 10 mA.
Check readout at max. (50 mA) and min. (10 mA) and fine tune
(tweak) as required per Step 8.
Example
2
(Negative
Slope):
A level measuring device puts out 6 mA when a storage tank is full and
15 mA when the tank is empty. The PAXLCL is to readout 90.0 tons at full
tank and zero when empty.
READOUT SPAN (Rs) = 900 - 0 = 900 (Disregard Decimal Points)
SWING CURRENT (Is) = 6 mA (@ max rdg) - 15 mA (@ min rdg) = -9 mA
In this case, the signal current is reversed [Term 3 (-) with respect to
Term 5 (+)] causing the readout to go “down” (increasingly negative) as
the negative current increases.
ADJUSTMENTS
Null the unit per Steps 1 to 4.
Set slope of transfer curve
with span adjustments to get
readout of -900 @ -9 mA per
Steps 5 and 6.
Move transfer curve up by
applying (+) offset per Step 7
until readout is +900 @ -6 mA.
Check extreme readings per
Step 8, 0 readout @ -15 mA
and +900 readout @ -6 mA.
Set D.P. Switch S1 and replace
unit in case.
Example
3
(±
Display):
A differential pressure transducer has a range of ±1500 PSI with a 4 to
20 mA output (-1500 @ 4 mA, +1500 @ 20 mA).
READOUT SPAN (Rs) = +1500 - (-1500) = 3000
SWING CURRENT (Is) = 20 mA (max) - 4 mA (min) = 16 mA
Note:
Since the display readout is limited to 1999 numerical
indication, the full READOUT SPAN of 3000 cannot be obtained
during zero based span adjustment. However, dividing both the
READOUT SPAN and SWING CURRENT by two, i.e. 1500
readout @ 8 mA, allows the span adjustment to be made for the
proper transfer curve slope.
ADJUSTMENTS
Null the unit per Steps 1 to 4.
Set transfer curve slope with span
adjustments per Steps 5 and 6, to
get a readout of +1500 @ 8 mA.
Apply (-) offset per Step 7 to get a
reading of -1500 @ 4 mA.
Check min. and max. extremes
and tweak if required to get desired
readout @ 4 and 20 mA per Step 8.
SPAN
OFFSET
CURRENT
(-)
4
MA
B
8
MA
20
MA
-1500
NULL
A
(+)
C
READOUT
+1500
D
CHECK
CHECK
D
1375
OFFSET
READOUT
NULL
40
B SPAN
10
50
MA
MA
MA
CURRENT
D
CHECK
C
A
C
A
D
CHECK
READOUT
B
CURRENT
(+)
(-)
-15
MA
-9
MA
-6
MA
-900
+900
OFFSET
NULL
SPAN
