Turbidity; Slope Calibration - Turbidity - Emerson Rosemount 1056 Instruction Manual

Instruction Manual
LIQ-MAN-1056

7.10 Turbidity

7.10.1 Description
This section describes how to calibrate the turbidity sensor against a user-prepared standard as a 2-point calibra-
tion with di-ionized water, against a 20 NTU user-prepared standard as a single point calibration, and against a
grab sample using a reference turbidimeter.
THIS SECTION DESCRIBES HOW TO CALIBRATE THE MODEL 1056 WITH AN ATTACHED TURBIDITy
SENSOR AS PART OF THE COMPLETE CLARITy II TURBIDITy SySTEM. THE FOLLOWING CALIBRATION
ROUTINES ARE COVERED.
Table 7-12 Turbidity Calibration Routines
Calibration function:
Measure Sec.
Turbidity
7.10.2 Slope Calibration
7.10.3 Standardize Calibration
7.10.4 Grab Calibration
A detailed flow diagram is provided at the end of Sec. 7 to guide you through the calibration routines.
To calibrate Turbidity:
1. Press the MENU button
2. Select Calibrate. Press ENTER.
3. Select Sensor 1 or Sensor 2 corresponding to
Turbidity. Press ENTER.
4. Select Turbidity. Press ENTER.
The following sub-sections provide you with the initial
display screen that appears for each calibration rou-
tine. Use the flow diagram for Turbidity calibration
at the end of Sec. 7 and the live screen prompts to
complete calibration.
7.10.2 SLOPE CALIBRATION — Turbidity
This section describes how to conduct a 2-point cali-
bration of the turbidity sensor against a user-prepared
20NTU standard. The calibration requires two steps.
First, immerse the sensor in filtered water having very
low turbidity and measure the sensor output. Next,
increase the turbidity of the filtered water by a known
amount, typically 20 NTU, and measure the sensor
output again. The analyzer takes the two measure-
ments, applies a linearization correction (if necessary),
and calculates the sensitivity. Sensitivity is the sensor
output (in mV) divided by turbidity. A typical new sen-
sor has a sensitivity of about 10 mV/NTU. As the sen-
sor ages, the sensitivity decreases. The figure below
illustrates how turbidity calibration works. Before
beginning the calibration, the analyzer does a dark
current measurement. Dark current is the signal gener-
ated by the detector when no light is falling on it. The
analyzer subtracts the dark current from the raw scat-
100
default value Description
Slope cal with pure water and a standard of known turbidity
Standardizing the sensor to a known turbidity
Standardizing the sensor to a known turbidity based on a
reference turbidimeter
The following screen will appear.
tered light signal and converts the result to turbidity. In
highly filtered samples, which scatter little light, the
dark current can be a substantial amount of the signal
generated by the detector.
Section 7.0: Calibration
S1: 1.234µS/cm 25.0ºC
S2: 12.34pH 25.0ºC
SN Calibrate?
Turbidity
S1: 1.234µS/cm 25.0ºC
S2: 12.34pH 25.0ºC
SN Calibrate
Slope
Standard
Grab
April 2017