Dual Slope Calibration - Emerson Rosemount Analytical HART 5081-A-HT Instruction Manual

MODEL 5081-A

10.4 DUAL SLOPE CALIBRATION

Figure 10-2 show the principle of dual slope calibration. Between zero and concentration C1, the sensor response
is linear. When the concentration of chlorine becomes greater than C1, the response is non-linear. In spite of the
non-linearity, the response can be approximated by a straight line between point 1 and point 2.
Dual slope calibration is rarely needed. It is probably useful in fewer than 5% of applications.
1. Be sure the transmitter has been configured for
dual slope calibration. See Section 7.8.
2. Zero the sensor. See Section 10.2.
3. Place the sensor in the process liquid. If auto-
matic pH correction is being used, calibrate the
pH sensor (Section 13.0) and place it in the
process liquid. If manual pH correction is being
used, measure the pH of the process liquid and
enter the value. See Section 7.8. Adjust the
sample flow until it is within the range recom-
mended for the chlorine sensor. Refer to the
sensor instruction sheet.
CALIBRATE
Sensor Cal
EXIT NEXT ENTER
CALIBRATE
Cal pt1
EXIT NEXT ENTER
CALIBRATE
time delay
EXIT NEXT
CALIBRATE
Grab spl
EXIT ENTER
58
4. Press CAL on the remote controller. Press NEXT.
5. The SEnSor CAL prompt appears. Press ENTER.
6. The CAL Pt 1 prompt appears. Adjust the chlorine concentration until it
is near the upper end of the linear range of the sensor. Press ENTER.
7. The tiME dELAy message appears and remains until the sensor read-
ing meets the stability criteria set in Section 7.8. To bypass the time
delay, press ENTER.
As soon as the stability criteria are met (or ENTER is pressed
to by-pass the time delay), the transmitter stores the sensor
current. Therefore, if the chlorine level in the process liquid
drifts while the sample is being tested, there is no need to
compensate for the change when entering test results.
8. The GrAb SPL (grab sample) prompt appears. Take a sample of the
process liquid and immediately determine the concentration of free
chlorine in the sample. Press ENTER.
CALIBRATION - FREE CHLORINE
FIGURE 10-2. Dual Slope Calibration
NOTE
SECTION 10.0