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6.1.5.

Adjusting the Position Output Scale Factor and the AGC Linearity

The Position Output Scale Factor is precisely adjusted at Cambridge Technology and under

normal circumstances never needs adjusting by the customer for the life of the servo board or

scanner. If however the customer has changed the scanner originally sent with the servo board,

(remember they are matched sets) use the following procedure to verify/adjust this signal.

The most important signal generated on the 670 board is the Position Output, Vp, signal. In

order for the servo and the error protection circuitry to work correctly, the Vp signal must be

scaled properly. The Position Output Scale Factor is conttolled by increasing or decreasing the

AGC voltage sent to the scanner's position detector. The Position Output Scale Factor is linearly

proportional to this AGC voltage. Thus, changes in the Position Output Scale Factor causes

changes in the amount the scanner will move for a given output response from Vp. R13 is used

to adjust this AGC signal. This trimpot allows-10% adjustment range. If

the

AGC voltage is

changed by more than

during this adjustment, the tuning ofthe system must be verified to be

sure that it is still set properly. It is always pmdent to check the tuning after any adjustment to

the Position Output Scale Factor or the Linearity Adjustment.

The Linearity Adjustment is used to improve the linearity of the position detector and position

demodulator. By varying the amount that Va and Vb sums together to create the AGC voltage,

the linearity is improved. The intention of

this

adjustment is to minimize the amount the AGC

voltage varies as a function of the angular position of the scanner. Since the Linearity

Adjustment and the Position Output Scale Factor adjustments affect each other, they must both

be set at the same time.

Note: Do not allow the AGC signal present at TP7 to exceed 11 volts or the AGC circuit may

saturate, which would result in improper operation.

••Caution: In all cases, the position signal, Vp, must always have the ability to exceed +/-10

volts when the scanner shaft is tumed to its intemal mechanical stops or scanner damage may

occur.

6.1.5.1

Closed Loop Method

If the system is afready tuned up and verification or "touching up" of the Position Output Scale

Factor and Linearity Adjustment are desired, use of this method is allowed. Also, if mixing and

matching scanners, this method can be used. A mirror must be mounted on the scanner shaft, or

some other means of measuring the scanner's angular position must be employed. By reflecting a

laser beam from the mirror to a wall, and using some simple trigonometry, the Position Output

Scale Factor can be adjusted with high resolution. The further from the wall, the more accurate

this method.

Follow steps

- 7 in section 4.2. above. Set up the input for analog single ended operation

by setting Jl and W4 as indicated in section 3.6.

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