DSC74 is a Vaisala sampling cell for connecting DM70 to pressurized processes (optional accessory). With DSC74B and DSC74C, measuring can be done in overpressure or atmospheric pressure. This depends on whether the sample gas is let into the sample cell before the needle valve or after that. See Figure 21 and Figure 22.
The DSC74 sampling cell comes with a quick connector that fits to industry standard compressed air line connectors (suitable for type D, Quick08, NIP08). This allows for easy installation and detachment of the probe without having to shut down the process. Alternative ways to connect are through the 2 different thread adapters (G3/8" to G1/2" and G3/8" to G1/4" ISO) that are supplied with each DSC74 unit.
| CAUTION If you use the thread adapters, the process pressure must be shut down for the installation or removal of the probe. If you use the quick connector, the process pressure can be maintained during the installation or removal of the sampling cell. Take a firm hold of the device to keep it in your hands while removing it. |
To connect to a pressurized process using DSC74:
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Make sure that the valve of the sampling cell is open. First close the valve, then turn it halfway open again. You can also first open the valve more to ventilate the parts, then readjust
it to allow only a small leakage.
Figure 1. Turning sampling cell valve screw with flathead screwdriver 
To verify that the leak screw is open, close the screw and then listen for a barely audible hiss when reopening the screw (1/2 turn). A light air flow can be felt when placing a hand over the opened valve.