Hach ORBISPHERE 3658 Basic User Manual page 17

Measurement mode
Choose Measurement Mode from the Configuration menu to enable maximum measurement
mode for sampling in bottles and cans.
In Maximum measurement mode, the instrument searches for two consecutive measurements with
less than a 2% difference, as also described in
the display is frozen and you may store the data. The instrument remains in this mode until you
select Normal measurement mode.
Calibration
Barometric pressure sensor calibration
You must have access to an accurate barometer to calibrate the instrument's internal barometric
pressure sensor. This is done using the Hach 3658 program on the PC. Choose Troubleshooting,
Pressure Calibration and a message will warn you that the current calibration will be lost.
Choose OK to continue. The calibration procedure then displays a Pressure Calibration dialog box.
The Measured Pressure value shows the current instrument pressure reading.
Enter the current atmospheric pressure, in mbars, in the Calibration Pressure entry box. Choose
Calibrate to direct the instrument to read and display the Measured Pressure using this calibration
value. Choose Quit when you are satisfied with the pressure calibration to return to normal
operation.
Sensor calibration
The TC sensor can be calibrated in a liquid sample with a known concentration of dissolved CO
in pure CO gas at atmospheric or elevated pressure. The following table gives information regarding
2
the different methods.
Calibration Method
Liquid CO solution
2
Gas at atmospheric
pressure
Gas at elevated
pressure (2-3 bar)
Before calibrating check that the sensor membrane surface is tight, smooth and wrinkle free. Select
the gas measurement phase for calibration (for full details see
Next, select the calibration medium using the Hach 3658 program (see
on page 16).
Ensure that normal measurement mode is selected in the Measurement Mode menu of the Hach
3658 program (see Measurement mode
Calibration must only be carried out once the TC sensor is giving a stable measurement. Expose the
membrane to the calibration sample until this stable reading is obtained. This usually takes about
5 minutes.
For calibration it is important that the sensor's membrane is at the same temperature as the
calibration sample. Therefore, allow some sample to pass through the flow chamber for 3 minutes
before calibrating.
Using the high precision calibration kit
Using the ORBISPHERE High Precision Calibration Kit, calibration and validation of the instrument
can be carried out quickly and easily. This ensures that each measurement of dissolved CO
true and accurate reading which is essential to final product quality.
Table 1 Sensor calibration information
Time Benefits
5 min High accuracy (for liquid
analysis)
5 min Quick and easy
10 min Higher accuracy than
atmospheric method.
Validation of the sensor
linearity
on page 17).
Measurement mode on page 10. When this occurs,
Drawbacks
Sensor linearity
validation not possible
Less accurate than
other methods
Requires a certified
pressure gauge
Gas measurement phase
Reference
ORBISPHERE High
Precision Calibration Kit
Gas with known purity,
certified barometer
Certified pressure gauge
on page 15).
Calibration medium
2
English 17
, or
2
gives a