Precision Measurement Engineering, Inc.
Dummy sensors should be installed whenever a sensor is damaged or removed. All of SCAMP's channels, except uDO, require that a sensor or a dummy sensor be connected. It is obvious that if no sensor or dummy sensor is connected to a channel then the reading on that channel will be incorrect. It is not so obvious, but true, that the readings on the other channels will also have serious errors even if sensors or dummy sensors are properly connected.
SCAMP is supplied with a dummy sensor kit, PME part number
5637. Two T sensor dummies and two C dummies are supplied. These can be
installed on either Fast or Accurate circuits. The dummy wire colors correspond to
the same colors on the actual sensor. Installation is obvious: remove the existing
sensor and install the dummy sensor wires to the same pins according to the color
connection for the existing sensor. If the existing sensor is already removed and
the color connection is lost, then see the fast temperature sensor connection diagram, accurate temperature sensor connection diagram or the conductivity sensor connection diagram. Wire-wrap wires to
circuit posts using the tool provided. Do not solder!
Broken sensors can be left physically connected to the
SCAMP or removed and replaced with a plug. Two sensor plugs are supplied with the Spare Seal kit. Remove the sensor and replace it with the
plug. The sensor plug is installed in the same way that a sensor is installed. See Replacing a Sensor section for more information. Normally
you will not have to replace the plastic ferrule that provides the seal around the sensor
shaft. One important note: Be sure to insert the plug
fully into the SCAMP end cap so that it extends very slightly within SCAMP's electronics
case, then TIGHTEN THE SENSOR RETAINING SCREW (a stainless set screw in SCAMP's
chassis). The picture below shows the location for this screw although it shows a
real sensor and not a dummy plug.
When SCAMP is submerged there is an external hydrostatic force that attempts to press the plug into the SCAMP. If the retaining screw is not tight, then the plug can slide into the SCAMP to the point where the ferrule seal releases allowing the SCAMP to become flooded.
Special note for SCAMPs having a Fluorometer installed. The dummy plug for a Fluorometer is longer than those supplied for other SCAMPs. Please insure that you have the right length. Sensor plugs should be long enough to penetrate slightly inside the SCAMP's electronic housing while still extending out through the sensor seal nut.
Tighten the ferrule compression nut as done with a normal sensor. Bubble test the SCAMP to insure that you've tightened it properly.
The software should be informed that a dummy sensor has been installed. This is not critical, but it may save confusion when the data are viewed subsequently. Use the SCAMP Control Dialogs Channel Tab to change the Sensor ID to Dummy. A note can be made in the Comments box as well. These will appear in subsequent *.txt profile files.