The GK-502 is designed to read both four-wire and six-wire full bridge load cells. Internal circuitry senses which type of load cell is connected and provides configuration for the appropriate load cell automatically. The output from the load cell is displayed in basic engineering units (digits, mV, mV/V) and is updated at a rate of one reading per second.
5:
Figure 5: GK-502 Readout
The GK-502 provides the ability to enter and store a gauge factor and zero reading for the load cell, which allows for an additional set of engineering units to be displayed (lb, kg, kip, tons, metric tons, and kN). An internal real-time clock/calendar is also included. The readout’s nonvolatile memory will store up to 999 time stamped readings. These stored readings can be displayed via the LCD display, or downloaded to a computer via the COM port for further analysis.
1.Connect the load cell to the readout box by means of the 10-pin input connector.
2.Push the ON/OFF button to turn on the readout.
3.If a load cell is not connected, or if there is a break in the cable between the GK-502 and the load cell, the GK-502 will display blinking dashes. if a load cell is detected, the GK-502 will begin taking readings.
4.The default Unit for the readings is digits (Dg). To change the unit, press the UNITS button. The options for units are:
5.Digits (Dg), which is proportional to the load.
6.The output voltage of the load cell in millivolts (mV).
7.The proportional reading of the load cell output voltage to the load cell excitation voltage (mV/V).
8.To store the reading to memory, push the STORE button.
9.Stored readings, along with the reading number and the date and time that they were taken are displayed by pressing the CFG to enter the Configuration menu. All stored readings may be downloaded to a computer for further analysis via the COM port.
10.Power the unit off by pressing the ON/OFF switch. The GK-502 will automatically power off after five minutes of operation.
For further information, please see the GK-502 Instruction Manual.
3.2Vishay Micro-Measurements P3 Readout Box
3.2.1Single Load Cell Load - Output in Engineering Units
To read a single load cell directly in engineering units complete the following:
1.From the main screen, select 'Bridge Type' and then select 'Ch 1 FB v opp'.
2.From the main menu screen and select 'Gauge Factor/Scaling'
a.Set the Units to lb, tons, or kilograms
b.Set the Full Scale to the full scale value of the load in engineering units taken from the geokon calibration sheet. E.g., if the load cell has a maximum calibrated load of 750,000 lb enter 375 tons in accordance with the units previously chosen. Note: Because the maximum allowable number here is 99999, lb units cannot be used if the full scale load is greater than 100,000 lb.
c.Set the F.S. mV/V to the Full Scale mv/V given on the geokon calibration sheet. If no value is given, then the mV/V Gauge Factor can be calculated by dividing the Full Scale change of digits by 4000. E.g., a load cell reads −237 at no load and 4216 at the full load of 750 kips the F.S. mV/V is (4452)/4000 = 1.113 mV/V.
d.Set the Dec. Places to the correct number in accordance with the Units and the Full Scale reading previously chosen.
3.Record the no-load zero reading, it may be needed later.
4.Go back to the main Menu screen and select 'Balance'.
5.Select the Mode: Auto and press the Balance button on the faceplate.
6.Press the balance button on the face panel a second time to select auto. This will trigger the auto balance procedure, which when completed will automatically bring up the Saving Settings menu.
7.Save the settings by pressing the Record button on the faceplate.
8.The P3 readout box display should now read zero and is ready to display the load directly in the engineering units chosen.
This configuration must be erased if the P3 readout box is used in a similar manner with a second load cell. To erase the settings, do the following:
1.Go to the Main Menu.
2.Select Options, Advanced, and then Factory Defaults.
3.Press the Record Button on the face panel.
Note: The auto balance feature only works when the load cell is under zero load. The readout cannot be switched from one load cell to another if the load cells are under load.
For more information, see the P3 instruction manual.
The simplest way to read multiple load cells using the P3 readout box is to read the output in mV/V and then use the mV/V gauge factor calculated as shown in Figure 4.2.
The P3 set up procedure is as follows:
Select Channel 1 from the main menu.
1.Select Bridge type FB v opp.
2.Select Gauge Factor Scaling units mV/V.
3.Select Balance, Chan: 1, and then Disable.
Important! If auto balance or manual balance is chosen, the settings for one load cell will carry over to the next. In addition, it is only possible to use the auto or manual setting when the load cell has no load on it. Auto balance must not be initiated with a load cell already under load.
4.The readings will be in mV/V. The linear gauge factor, given by the calibration sheet in engineering units, can be multiplied by 4000 to convert mV/V to engineering units.
For more information, see the P3 instruction manual.