Victoreen 875

Operators Manual

8

L

Connected to 4

12

L

 

10

H

Since U202, (8, 9, 10) is

11

H

Because 12 and 13 are L

NOR

 

 

 

 

 

12

H

Result: Output switches

 

 

This is the original condition. No

from Low to High

 

 

change takes place.

 

 

 

 

Notes:

1)Enable pulse assumed present, so 1 and 5 are L.

2)Initial condition assumes 12 and 10 L.

The truth table shows that no change in the output can occur without the presence of the enable pulse, even though the monitoring signal indicates a fail condition. This is necessary because the ramp voltage starts from zero during the ECS Test.

Table 5-2.

Signal In Fail State (High Signal Input)

 

 

 

 

Pin 1

 

Voltage State

Comments

10, U208 and 6, U202

H

Fail state

9, U208 and 2, U202

L

After inversion

1,5, U202

 

H

No enable input

4, 8, U202

 

L

Because of NOR action

3, 13, U202

 

L

Because of NOR action

10, 12, U202

 

L

Because of NOR action

 

 

 

 

Thus the circuit does not react to a fail signal input unless pins 1 and 5 are low.

NOTE

If a problem cannot be resolved by applying the troubleshooting and maintenance procedures provided here, please contact Fluke Biomedical at 440.248.9300 for assistance.

5-12

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Image 42
Fluke 875 manual Nor, Pin Voltage State Comments