51
9900 Transmitter
N
O AVERAGING, NO SENSITIVITY
With SENSITIVITY set to 0 (zero) and AVERAGING set to OFF (0 seconds), the 9900 responds immediately to
every shift in the process. The dashed red line represents the actual output of the sensor in varying conditions.
AVERAGING ONLY
With SENSITIVITY still set to zero and AVERAGING set to MED or HIGH the rate is stabilized, but a sharp change
in rate is not represented for 8 to 32 seconds or longer.
AVERAGING AND SENSITIVITY
With SENSITIVITY at 50 and AVERAGING set to MED or HIGH, the rate is stabilized, while a sudden shift in
fl
ow
rate exceeding 50 units of measure will be displayed immediately.
NOTE:
The SENSITIVITY function applies only to FLOW.
The SENSITIVITY function has no effect if the AVERAGING function is set to OFF.
5 s
0 s
10 s
15 s
20 s
25 s
30 s
35 s
Averaging is different depending on the measurement type.
Seconds to 99.5% of Final Value for Low, Med, and High are:
Sensor Type
Low
Medium
High
Flow
10
40
120
pH
2
4
12
ORP
2
4
12
Cond/Res
4
6
12
Pressure
4
10
30
Level/Volume
4
10
30
Temperature
3
10
30
4 to 20 mA
4
10
30
Salinity
4
6
12
In Conductivity/Resistivity, the logarithmic (LOG) mode can be used when a very large measurement range is required,
yet high resolution is needed at the low end (e.g. in a clean-in-place application where a high-resolution conductivity
reading is needed at the low end, while a very high conductivity reading is needed when a cleaning cycle is in progress).
Only two parameters need to be set up, the starting or base conductivity value (4 mA SETPNT) and the ending or
maximum conductivity value (20 mA SETPNT). The 4 mA setpoint may be larger than the 20 mA point (reverse span).
What equation should be put in the PLC?
Conductivity = 10
n
n
= (mA input – 4.0) ×
(Log
10
20 mA setpnt – Log
10
4 mA setpnt)
+ Log
10
4 mA setpnt
16 mA
If only
fi
xed thresholds are of required, they can be calculated in mA. Then the mA value can be checked directly.
Inside the 9900 the following equation is used:
mA = (Log
10
Conductivity – Log
10
4 mA setpnt) ×
16
+ 4
(Log
10
20 mA setpnt – Log
10
4 mA setpnt)
NOTE:
If ADJUST 4 mA or ADJUST 20 mA is used, the mA value can be affected. To prevent any problems the adjust function
should only be used to get exactly 4.0 and 20.0 at the PLC. The 9900 is accurate and the adjust functions are only needed
to compensate for an offset due to noise or a not-so-accurate PLC input card.
The error value of either 3.6 mA or 22 mA should be tested
fi
rst before applying the conductivity equation.
Appendix
LOG Current Loop Output
Averaging
