YOKOGAWA DPharp EJXC40A, Руководство пользователя

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<7. HART Communication>
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IM 01C25W05-01EN
c) Using the external zero-adjustment screw
Parameter Ext SW can be used to enable or
disable the zero point adjustment using the
zero-adjustment screw on the transmitter.
To use the zero-adjustment screw, select
Enabled (the factory default setting is Enabled).
For the setting procedure, see subsection
7.2.3.11.
While viewing the output value, turn the
zero-adjustment screw on the outside of the
transmitter case using a slotted screwdriver
so that the output value is set to zero. Turn
the screw clockwise to increase the output
or counterclockwise to decrease the output.
The zero point adjustment can be made with a
resolution of 0.01% of the setting range.
Since the degree of zero adjustments varies
with the screw turning speed, turn the screw
slowly for fine adjustment and quickly for coarse
adjustment.
F0708.ai
Zero-adjustment screw
Figure 7.2.5 Zero-adjustment Screw
(2) Span Adjustment for Differential Pressure
Span adjustment changes the input/output
characteristics with the low limit of the measuring
range (zero point) as the reference. Therefore,
be sure to perform span adjustment (high limit
adjustment) after zero point adjustment (low limit
adjustment). There are two adjustment methods:
automatic and manual.
a) Automatic adjustment
If you apply pressure for the point you want
to adjust and enter the pressure value in
a parameter, the transmitter automatically
calculates the adjustment value and makes
appropriate adjustments.
• Recalling and setting automatic adjustment
parameters
Recall
parameters
[Root menu] → Maintenance → DP trim
→ DP trim (method)
Auto, Lower
Pt
Set the low limit value you want to
adjust.
Auto, Upper
Pt
Set the high limit value you want to
adjust.
Select Auto, Lower pt. parameter to adjust the lower
limit.
Apply the reference pressure that corresponds to
the low limit of the transmitter’s measuring range,
and confirm the value when the reference pressure
stabilizes.
Next, select the high limit adjustment parameter
“Auto, Upper Pt,” apply the reference pressure that
corresponds to the high limit of the transmitter’s
measuring range, and confirm the value when the
reference pressure stabilizes.
b) Manual adjustment
Manually calculate the zero point and span
adjustment value from the actually applied
pressure and the transmitter output. Then, set
parameters “Manual, Lower Pt” and “Manual,
Upper Pt” to those values. Assume that
adjustment for the 10 to 30 kPa range was
made in the past, and that the following zero
and span adjustments were used.
P LTD = −0.04 kPa, P UTD = −0.03 kPa
The settings for this example are indicated
below.
1. Recall low limit adjustment parameter Manual,
Lower Pt.
Recall
parameters
[Root menu] → Maintenance → DP trim
→ DP trim (method) → Manual, Lower
Pt
2. Apply the low limit reference pressure of 10 kPa
to the transmitter. We assume that the output
display at this point is 9.94 kPa.
3. The output difference (10 – 9.94 = 0.06 kPa) at
that point is added to the past adjustment value
(−0.04 kPa) to calculate the zero adjustment
value.
−0.04 + 0.06 = 0.02 kPa
4. Enter 0.02 for P LTD.
5. Next, recall high limit adjustment parameter
Manual, Upper Pt.
Recall
parameters
[Root menu] → Maintenance → DP trim
→ DP trim (method) → Manual, Upper
Pt