SCALING THE DP25-S TO A LOAD CELL USING CALIBRATION DATA

Example: A unidirectional 3000 lb load cell with a full scale sensitivity of 2.227 mV/V and 10 Vdc excitation

1. From the load cell calibration certificate.
Determine:
a. the excitation voltage required (usually 5 or 10 Vdc)
b. the full scale output (sensitivity) of the load cell at the excitation voltage (mV/V x excitation voltage = 2.227 mV/V x 10 V = 22.27 mV).

2. Go to page 10 in the manual (M1861/0698). Set the DIP switches for the proper excitation voltage and load cell output range.

Bi-directional load cells are typically the ±50 mV range. For a Bi-directional load cell with 10 Vdc excitation, the switch settings are 1,3,5, and 6 closed; with 5 Vdc excitation the setting are: 1,3,5,6, and 7 closed.
Note on bi-directional applications: the DP25-S only counts to ­1999 in the negative direction.

Unidirectional load cells (this example) are typically the 0-100 mV range. For a Unidirectional load cell with 10 Vdc excitation the switch settings are: 1, 3 and 6 closed; all others open; with 5 Vdc excitation the setting are: 1,3,6 and 7 closed.

3. Go to page 17 in the manual. Connect the load cell per figure 3-5. Check the load cell specification for proper wiring codes.
Note: Typical color coding of wire and connections to TB2 are:
Red = Excitation + (#2)
Black = Excitation ­ (#1)
Green = Signal + (#6)
White = Signal ­ (#7)

4. Go to page 23 in the manual. Follow the procedure in 4.1 and 4.2 to set the input range and decimal point position.

5. Go to page 26 in the manual. Select the value of RD.CF R.2. Find the value in the left column that is closest to but not smaller than the full scale output of your load cell. Select the R.2 value from the right column; i.e. for a load cell with a full scale output of 22.27 mV the R.2 value is 2
Go to page 49 to enter this value into the meter.
Press Menu 4 times, the meter should display RD.CF
Press Tare, R.1=R,
Press Tare, R.2=4 press NT/GRS to change the value or R.2 to the value determined in this example R.2=2.
Press menu to store the value, press reset twice to return to the run mode.

6. Go to page 29 in the manual, paragraph 4.3.2. To scale the meter in engineering units, the meter uses two point scaling. You enter four values, electrical inputs (IN1 and IN2 which are matched to Display values (RD1 and RD2). All you need to calculate is the value for IN2. Use the formula in bold type in the middle of page 29 (and below).
You need to know:
a. the load cell output in mV at full scale
b. the natural gain of the meter for the range selected (see table 4-3 page 29) 100 for the 0-100mV range, or 40 for the ±50 mV range)
c. the multiplier value effected by the value of R2. See table 4-4 on page 30.

IN2 = Sensor output x natural gain x R.2 Multiplier x 10/excitation voltage)
         (mV at full scale)
Using the example, a unidirectional load cell with a full scale output of 22.27 mV at full scale (unidirectional means the 0-100 mV range was selected). IN2 = 22.27 x 100 x 3.333 x 10/10 = 7422.6 (round to 7423)

For a typical load cell, zero output at zero load:
IN1 is 0000 (ignore the decimal point)
RD1 is 0000
IN2 you calculate using the formula on page 29 (7423 ignore the decimal point)
RD2 is the full scale display (in engineering units) at full scale (3000 for this example)

To enter these values (go to page 48 to see menu flow):
Press MENU 3 times ­ display reads RD.S.O
Press TARE ­ display reads IN1
Press TARE ­ display reads 0000 (the factory preset)
Press MENU ­ display reads RD1
Press TARE ­ display reads 0000 (the factory preset)
Press MENU ­ display reads IN2
Press TARE ­ display read 9999 (the factory preset) change this value to the calculated value (7423) using the NT/GRS button to change the flashing digit and the TARE button to move to the next digit. When entered
Press MENU ­ display reads RD2
Press TARE ­ Display reads 1000 (the factory Preset) change this value to engineering units (3000 for this example) using the NT/GRS button to change the flashing digit and the TARE button to move to the next digit. When entered
Press MENU to save settings
Press RESET twice to return to the run mode

7. The meter is now scaled to read 0-3000 pounds for an input of 0 to 22.27 mV. Since all load cells have small zero voltages, the meter will not be displaying 0000 when there is no load on the load cell but rather a small zero offset. To correct this, press the TARE button, with no load on the load cell, and the meter will display 0000. This will not affect the calibration.