EG&G ORTEC 775 Bedienings- en onderhoudshandleiding - Pagina 9

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the case of the count input connectors, no isolation is

provided between the two inputs; so two signal sources

should not be connected simultaneously. When there is no

connection to the Gate input, the sealer gate permits the

unit to operate. To cut the gate off, the gate input must be

pulled down below +1.5 V but not below —5 V. To do this,

the driving circuit must be capable of absorbing 0.5 mA

from the gate input circuit. The gate input circuit permits

counting when the gate input is at +3 V or greater.

Reset Input A reset input signal can be connected to the

775 through the rear panel BNC connector. To reset the

sealer to zero, a positive signal of +3 V or greater

originating from zero potential with a minimum width of

100 nsec should be used. The input impedance is approxi

mately 2 kfZ dc-coupled to ground. Negative signals will not

perform any useful function at the reset input. The input

circuitry wi ll not be harmed as long as the input signal level

does not exceed ±25 V.

Overflow Output The overflow signal is available through

a rear panel BNC connector. A positive 5-V signal appears

at the output each time the contents of the counter change

from 999 999 to zero. The output signal width is 2 /jsec. Zq

< 10Tl, dc-coupled.

4. OPERATING INSTRUCTIONS

4.1. FRONT PANEL CONTROLS AND INDICATORS

The following functions are indicated and controllable from

the front panel:

Count/Stop Manually controls counting of the 775; Count

position permits counting and Stop position inhibits

counting.

Gate Indicator An LED indicates the condition of the

input gate. When it glows, the 775 is able to count input

pulses. When it is dark, the 775 is inhibited from counting.

Reset A push-button switch resets the contents of the

counter to zero when it is depressed.

Discriminator A single-turn

potentiometer selects the

threshold level of the internal discriminator with a range of

100 mV through 10 V. Normally, for counting logic signals,

the level should be adjusted about half way between the

lowest expected true signal amplitude and the maximum

false signal amplitude. For use with l inear signals assure that

the signals have only one point of inflection, or some

signals may cross the threshold more than one time and

produce erroneous results.

Overflow Indicator An LED l ights if the counter capacity

of 999 999 counts is exceeded, and remains l ighted unti l

the unit is reset.

Display Test A push-button switch permits a quick check

of the digital display. When it is pressed, all seven segments

of each of the six digits wi l l be lighted, regardless of the

counter contents, and the display wi ll read al l "eights."

Digital Display Six 7-segment characters with logically

selected blanking for each segment display the counter

contents at all times except during the Display Test

interval. Each character can display a digit from 0

through 9.

4.2. INITIAL OPERATION OF COUNTER

1. Install the 775 into a 401/402 Series Bin and Power

Supply or equivalent and turn on the power.

2. Press Reset. The display should now indicate that the

contents of the counter are zero.

3. Press Display Test. The display should read

and should return to 0 when the switch is released

4. Set the Count/Stop switch at Count, and the Gate

indicator should light. Set the switch at Stop, and the light

should go out.

5. Connect a signal to the Input connector.

6. Set the Count/Stop switch at Count.

7. Turn the Discriminator control counterclockwise unti l

the 775 starts to count.

8. Ground the Gate input and observe that counting stops

and that the indicator LED is not l ighted. Remove the

ground and restore the counting condition.

9. Set the Count/Stop switch at Stop, and counting should

stop and the indicator again not be l ighted.

4.3. COUNTING SETUP WITH ONE COUNTER

Proceed as outlined in Section 4.2 but omit those steps

used in "testing" the instrument. Be sure that the input

signals do not exceed the ±25-V maximum limits.