B&B Electronics FBDA manual Gain Selection, Gain Jumper Selection

Chapter 3: Gain Selection

The FBDA has several different gain settings to provide the largest possible voltage range for an A/D converter. The gain of the FBDA is selected using a jumper, 6 jumper pins (labeled 1-6), and a potentiometer (labeled P1). The FBDA is calibrated at the factory to have a gain of 80 ± 2. To change the gain of the FBDA the following steps should be followed:

1.Remove the cover from the FBDA using a small slotted screwdriver.

2.There are six jumper pins labeled 1-6. Place the jumper on the two pins selected from Table 3.1 below. Placing the jumper on the two selected pins will set a gain near the values listed in Table 3.1.

3.Make all of the required connections (power supply, A/D converter, sensor, and excitation voltage), and turn on the power.

4.Set up your sensor to provide a known input signal for the FBDA. If you are using a load cell, place a known weight on the load cell. This will produce a known input signal.

5.The output voltage from the FBDA can be read from DB-25 pin 8 (A/D 0 on B&B Electronics’ SDAXX data acquisition modules).

6.Adjust P1 to trim the gain to an exact value. The gain equation is shown below. ((SIG+) - (SIG-)) is the input signal.

Table 3.1: Jumper Selection to Choose Gain

Gain	Jumper Selection
25	Jumper pin 5 to pin 6
40	Jumper pin 4 to pin 5
80	Jumper pin 2 to pin 3
220-1000	Jumper pin 1 to pin 2

1.The potentiometer (P1) becomes more critical as the gain is increased.

2.The gain range of 220 to 1000 is entirely decided by P1. When P1 is turned completely in counter-clock-wise, the Gain will be close to 220. When P1 is turned completely clock-wise, the Gain will be greater than 1000.

Documentation Number FBDA0797 Manual 7

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