IM-P402-84 AB Issue 6
11
The graphs can be used to check that the
calibration is correct by projecting up from the
pre-set steam calibration rise to confirm the
water level rise. Both methods of calculation
depend on an accurate assessment being made
of the rise in water level /change in set point
under full steam flow (maximum demand). This
rise in water level can vary according to
operating conditions, for example steady
maximum steam demand or intermittent,
sudden demand, and factors such as boiler
pressure and water TDS level. There will also
be a difference in level between the boiler and
the gauge glass under different firing conditions
and steam demands. Accordingly, further
adjustment to the settings may well be
necessary to achieve optimum performance. A
change in the pattern of steam demand, for
example when extra heating is needed in
winter, may also require the settings to be
adjusted.
Alternative graphical method of commissioning the steam input. (Probe with PA20 only)
Figure 6, (also shown on the controller front panel), and figure 7 offer a convenient, though less
accurate method of commissioning the steam input.
If the anticipated water level rise is:-
- less than 80 mm and the PA20 preamplifier is set to high sensitivity,
or
- less than 140 mm and the PA20 is set to medium sensitivity, then insert a range link between
terminals 4 and 5 of the LC2400 and use figure 6.
If the anticipated water level rise is:-
- greater than 80 mm and the PA20 is set to high sensitivity,
or
- greater than 140 mm and the PA20 is set to medium sensitivity, do not insert a range link and
use figure 7.
The graphs are used for a steam flowmeter with a change in output current of 16 mA (4-20 mA).
If a steam flowmeter has a fixed current output, use the following formula to scale the rise in water
level.
Scaled rise in water level (mm) =
Steam flow at 100% demand (kg /h)
x
Actual rise in
Maximum steam meter rating (kg /h) level (mm)
To commission the LC2400 using the graphs:-
The two curves on each graph correspond to the sensitivity settings selected in the connector of
the PA20 preamplifier.
- From the set point position on the gauge glass measure the required rise in water level caused
by a steam demand.
- Note where the rise in water level meets the relevant curve on the graph.
- Read off the steam calibration setting on the bottom line of the graph.
- Set the 'steam' potentiometer to the position indicated by the graph.
The following examples demonstrate how to use the graphs:-
Example 1. If the water level is expected to rise by 60 mm when there is a 100% steam demand,
and the preamplifier sensitivity is high, then the steam calibration setting is 8. (Figure 6, link fitted).
Example 2. If the water level is expected to rise by 300 mm and the pre-amplifier is set to
medium sensitivity, then the steam calibration setting of 3.5 is obtained from the upper curve in
figure 7. The link is not fitted in this case.
7. Calibration notes