Hach 3650 manual Taking Measurements, Preconditioning Sensor

3650 Portable O2 Analyzer - Operating Information 15 of 50

2.2 Taking Measurements

Once the system is calibrated, you should be able to begin taking measurements. Connect the top-mounted inlet to accept your sample, typically this is accomplished by connection to a sampling valve. The sample flow can be regulated by the knurled stainless steel knob on top of the flow chamber.

Minimum flow rates, measurement limits and response times for the various available membranes are given in the accompanying EC Sensors - Maintenance & Installation Manual.

The LCD includes a right-side marker to distinguish between gas concentration measurements and temperature. This marker also indicates the measurement display units (ppm, ppb or % depending on the instrument model).

To switch between gas measurement and temperature measurement, press the Up/ Down Arrow buttons.

To backlight the LCD for approximately three minutes, press the Backlight button.

Note:

For measurements of gaseous samples in % units, you must open the barometric pressure sensor relief valve switch on the top of the instrument from time to time, to allow the pressure inside the instrument to equilibrate to the barometric pressure.

2.2.1 Preconditioning Sensor

You can expect a more rapid and accurate first result if you precondition the sensor before you take readings.

To precondition, connect the flow chamber to a convenient sampling source at or below expected O2 levels. If measurements take place in carbonated samples, precondition with a carbonated beverage or carbonated water. Open the sampling valve on the flow chamber, just enough for a trickle. Then, switch on the instrument and watch the LCD. You will see the values drop.

If you are measuring in the 0.1 ppm range, then only a short time is required for the display to fall to this level, whereas ppb level measurements may require the sensor to remain exposed to the sample for half an hour or more. You will establish your own requirement with experience. Once the LCD displays the expected level of O2, close off the sample. The sensor is now preconditioned and ready to use.

You may want to precondition prior to each series of measurements, depending on frequency of use.

Operator Manual ORBISPHERE