User`s guide

Calibration • 53

6.2 VR Assignments

There are five variable resistors (VR) on the ACL-8111 board to allow

you making accurate adjustment on A/D and D/A channels. The

function of each VR is specified below:

VR No. Function

VR1 D/A full scale adjustment

VR2 D/A zero offset adjustment

VR3 A/D offset adjustment

VR4 A/D full scale adjustment

VR5 A/D programmable amplifier offset adjustment

6.3 D/A Calibration

The D/A input reference voltage should be connected to for

calibration. You may use the JP1 to select the -5V or -10V reference.

The zero offset and full scale of D/A channel can be turned through

VR1 and VR2. The full-scale gain of D/A is adjusted by VR1, and zero

offsets are adjusted by VR2.

Note: A precision voltmeter to measure the D/A output is very important.

The procedures of calibration are as follows:

•

Full scale adjustment:

1. Set JP1 to select -5V as reference voltage.

2. Connect VDM (+) to CN1 pin 30 and VDM (-) to A.GND.

3. Write digital data '4095' (0x0FFF) into D/A's digital data

4. Adjust VR1 until your voltmeter's voltage reading is equal to

+5V (reference voltage with opposite sign).

•

Offset zero adjustment:

1. Write digital data ' 0' (0x0000) to D/A's digital data register

(BASE+4 and BASE+ 5).

2. Adjust VR2 until the your voltmeter's voltage reading is 0V.