6.Taking Readings

6.1Strain Gauge Readout Positions

table 1: Strain Gauge Readout Positions

6.2GK-404 Vibrating Wire Readout

The Model GK-404 VW Readout is a portable, low-power, hand-held unit that is capable of running for more than 20 hours continuously on two AA batteries. It is designed for the readout of all geokon vibrating wire instruments, and is capable of displaying the reading in digits, frequency (Hz), period (µs), or microstrain (µε). The GK-404 also displays the temperature of the transducer (embedded thermistor) with a resolution of 0.1 °C.

17:    

Figure 17: GK-404 Readout

6.2.1Operating the GK-404

1.Attach the flying leads by aligning the red circle on the silver Lemo connector with the red line on the top of the GK-404 (see the figure below). Insert the Lemo connector into the GK-404 until it locks into place.

18:    

Figure 18: Lemo Connector to GK-404

2.Connect each of the clips on the leads to the matching colors of the sensor conductors, with blue representing the shield (bare).

3.To turn on the GK-404, press the On/Off button on the front panel of the unit. The initial startup screen will display.

4.After a delay, the GK-404 will start taking readings and display them based on the settings of the Pos and Mode buttons.

The unit display (from left to right) is as follows:

■The current position: set by the Pos button, displayed as A through F.

■The current reading: set by the Mode button, displayed as a numeric value followed by the unit of measure.

■Temperature reading of the attached instrument in degrees Celsius.

Use the Pos and Mode buttons to select the correct position and display units for the model of equipment purchased (see Section 6.1).

The GK-404 will continue to take measurements and display readings until the unit is turned off, either manually or by the Auto-Off timer (if enabled).

For more information, consult the GK-404 manual.

6.3GK-405 Vibrating Wire Readout

The GK-405 Readout is made up of two components:

■The Readout Unit, consisting of a Windows Mobile handheld PC running the GK-405 Vibrating Wire Readout application.

■The GK-405 Remote Module, which is housed in a weather-proof enclosure.

The remote module can be wire-connected to the sensor by means of:   

■Flying leads with alligator clips if the sensor cable terminates in bare wires.

■A 10-pin connector.

The two units communicate wirelessly using Bluetooth^®, a reliable digital communications protocol. Using Bluetooth, the unit can operate from the cradle of the remote module, or, if more convenient, can be removed and operated up to 20 meters away from the remote module.

The GK-405 displays the thermistor temperature in degrees Celsius.

For further details, consult the GK-405 Instruction Manual.

Figure 19: GK-405 Readout

6.3.1Connecting Sensors with 10-Pin Bulkhead Connectors Attached

Align the grooves on the sensor connector (male), with the appropriate connector on the readout (female connector, labeled senor or load cell). Push the connector into place, and then twist the outer ring of the male connector until it locks into place.

6.3.2Connecting Sensors with Bare Leads

Attach the flying leads to the bare leads of a geokon vibrating wire sensor by connecting each of the clips on the leads to the matching colors of the sensor conductors, with blue representing the shield (bare).

6.3.3Operating the GK-405

Press the power button on the Readout Unit. After start-up completes, a blue light will begin flashing, signifying that the two components are ready to connect wirelessly. Launch the GK-405 VWRA program by doing the following:

1.Tap Start on the hand-held PC's main window.

2.Select Programs.

3.Tap the GK-405 VWRA icon.

After a few seconds, the blue light should stop flashing and remain lit. The Live Readings window will display on the hand-held PC.

Set the Display mode to the correct letter required by your equipment (see Section 6.1).

For more information, consult the GK-405 Instruction Manual.

6.4Measuring Temperatures

All geokon vibrating wire instruments are equipped with a thermistor for reading temperature. The thermistor gives a varying resistance output as the temperature changes. The white and green leads of the instrument cable are normally connected to the internal thermistor.

The GK-404 and GK-405 readouts will read the thermistor and display the temperature in degrees Celsius.

To read temperatures using an ohmmeter:

1.Connect an ohmmeter to the green and white thermistor leads coming from the instrument. Since the resistance changes with temperature are large, the effect of cable resistance is usually insignificant. For long cables a correction can be applied equal to approximately 48.5Ω per km (14.7Ω per 1000') at 20 °C. Multiply these factors by two to account for both directions.

2.Look up the temperature for the measured resistance in Appendix C.