DAC Circuit Board - User Guide
   
 
 
Introduction
Functional Description
Connecting the DAC
Calibration
 

 

Technical Specification
 
Inputs:-
8 bit binary word for signal strength
single bit binary for control signal
Ground and +5V for DAC board power
 

Outputs:-
Unipolar mode
Nominal 0v to +5v
Maximum 0v to +10v

Bipolar mode
Nominal -2.5v to +2.5v
Maximum -5v to +5v
 

Connections
Input:-
IDC 10 way header for signal strength and board power
Rising clamp screw terminal for control signal

Output:-
Two rising clamp screw terminals for analogue output.
 

Size:-
Approx 90mm x 45mm
(not including ribbon cable)

 

Calibrating the DAC

There are a number of steps to go through in calibrating the DAC to provide the exact outputs that you are asking it to send. The next set of instructions assumes that you are running Motion Drive software and that you have connected the DAC and USB modules to your PC and that no other motion platform equipment is connected. Having done that open the platform configuration setting sheet and set the DAC mode to 1 (for unipolar). Save the settings and then open the sheet for Manual Operation. Change the operation mode to Operate Drives Individually.

For the calibration operation you will need an electrical screwdriver and a digital voltmeter (DVM) (obtainable at any good electrical or hobby store). Connect DVM across the GND terminal and the Test Point (TP1) initially. Later you will connect your DVM across the output terminals of the DAC (GND and OUT). Calibration is carried out by adjusting the settings on VR1 to VR4 on the DAC board. Adjusting the setting is done by turning the tiny adjustment screw on each of those components.


Unipolar Calibration

Set the switch SW1 to U for unipolar mode.

Step One.
On the Manual Operation sheet, set the output for the appropriate drive (the one to which the DAC is connected) to 0 for Power and set the Duration to 5000. Click on Drive Platform.

With the DVM connected across GND and TP1, adjust VR2 until it shows as close to 0.00v as possible.

Then connect the DVM across the output terminals (GND and OUT) and adjust VR4 until it shows as close to 0.00v as possible.


Step Two
Keeping the Duration at 5000, set the Power to 255. Click on Drive Platform.

Adjust VR1 until DVM shows 5.10v. Each run gives you 5 seconds to make adjustments, so you may have to perform more than one run to achieve the right adjustments.

Check linearity by setting the Power to intermediate values (eg 128, 64). Repeat steps one and two if necessary.

Bipolar Calibration

Unipolar calibration must be done before this can be done. Set the Switch SW1 to B for bipolar operation.

Step One
Set power to 0. With Duration set to 5000, click on Drive Platform. The reading on DVM should be -2.56v. If not adjust VR3 until it shows -2.56v.

Step Two
Set power to 255. Click on Drive Platform.

Adjust VR4 so that DVM reads +2.54v

Step Three
Close the Manual Operation window. Open Platform Settings, and change DAC mode to 2 (for the CF DAC). Click on Apply Current (or Save Current then Apply Current if you wish to save that setting). Open the Manual Operation window again and select Operate Drives Individually. Check outputs with Duration of 5000 and Power settings at -255, 0 and 255. Power setting of -255 should give -2.56v, 0 should give 0v and 255 should give +2.54v.

As above, check linearity with intermediate values.

Voltage Ranges

The above instructions are to calibrate the DAC for the nominal ranges of 0 to +5V in unipolar operation and -2.5v to +2.5v in bipolar operation. If your MCBs require a larger span, then it is possible to increase the ranges to 0 to 10v and +-5v to +5v respectively. See below for details.

Increased Unipolar Range
Calibrate the DAC for 0.00v as above. Then, keeping the Duration at 5000, set the Power to 255. Click on Drive Platform. Adjust VR1 until you get the desired output voltage for full scale (up to 10.00v).

Increased Bipolar Range
Carry out Unipolar calibration as above and also step one of bipolar calibration routine. Then with the Power setting on 255, adjust VR1 and VR4 to achieve the bipolar range you require (up to -5V to +5V). VR1 is to be adjusted to increase the negative range from -2.5v to -5v, while the manual operation is not running (in between clicking on Drive Platform). VR4 is to be adjusted to increase the positive range from +2.5v to +5v while the manual operation is running (the 5 second run). You will need to adjust them together as they affect each other, but with patience you can achieve the increased range you require.

Check intermediate values and correct range as step three above checking that the new full scale readings are correct for -255 and 255 Power settings. Having adjusted VR1, the DAC will need to be recalibrated from scratch should you wish to use it in Unipolar mode.
 
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© Active Simulation Limited 2007

DAC circuit board User Guide version 1.0