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20 nsec minimum to be counted. Zjp 1 kS2 to ground,

dc-coupled.

Gate

Front and rear panel type BNC connectors accept

standard positive logic signal to control the counter gate

and the associated indicator. Open circuit or >+3 V to

allow counting; <+1.5 V to inhibit counting; 25 V

maximum; driving source must be capable of sinking 0.5

mA of positive current.

Reset Rear panel type BNC connector accepts standard

positive logic pulse to reset the unit to an initial zero

condition. >+3 V resets; <+1.5 V does not reset; 25 V

maximum; 100 nsec width minimum.

2 kfi dc-coupled

to ground.

Overflow Rear panel type BNC connector furnishes stand

ard positive logic output, +5 V for 2 /tisec, whenever the

counter overflows from 999 999 to 0. Driving source

impedance <1 Of2 dc-coupled.

2.5. ELECTRICAL AND MECHANICAL

Power Required For the 775 Counter: +25 V, 95 mA;

—1 2 V, 20 mA; 11 5 V ac, 50 mA, 50 or 60 Hz.

For the 775 H Counter: + 12 V, 95 mA; —12 V, 20 mA; +6

V, 550 mA.

Dimensions Standard NIM single-width module (1.35 by

8.714 in.) per TID-20893.

3. INSTALLATION

3.1. GENERAL

3.3. SIGNAL CONNECTIONS

The 775 operates on input power that must be furnished

from a Nuclear-standard Bin and Power Supply such as the

ORTEC 401/402 Series. If any vacuum tube equipment is

operated in the same rack with the 775, there must be

sufficient cooling air circulating to prevent any localized

heating of the integrated circuitry used throughout the 775.

The temperature of equipment mounted in racks can easily

exceed the maximum l imits of 120°F (50 C) unless

precautions are taken.

3.2. CONNECTION TO POWER

Turn off the Bin Power Supply when inserting or removing

any modules. The ORTEC modules are designed so that it is

not possible to overload the Power Supply with even a ful l

complement of modules in the Bin. Since, however, this

may not be true when the Bin contains modules other than

those of ORTEC design, the Power Supply voltages should

be checked after al l

modules have been inserted. The

401/402 has test points on the Power Supply control panel

to permit monitoring the dc voltages easi ly.

The 775 requires 11 5 V ac as one of its power inputs. Some

bins and power supplies, as wel l as jumper cables, may not

be wired to include this power. In the event that the unit

fails to operate in a new installation, check the bin and/or

cable to determine whether the 11 5-V ac circuit is included.

The 775H version requires +6 V at 550 mA. It must be

used with an ORTEC 401 B/402H Bin and Power Supply or

equivalent to satisfy this power requirement. No ac power

is required for the 775H.

Count Input The signal to be counted by the 775 can be

connected to either the front or rear panel BNC connector.

These two connectors are not isolated from each other;

signals from two sources should not be used and connected

simultaneously to the two input connectors.

The input circuit of the 775 is dc-coupled to eliminate

baseline shifts associated with changing counting rates. For

signals whose average dc level is greater than ±25 V,

external capacitive coupling must be provided by the user.

For dc levels below 25 V, connection can be made to the

input safely without damage to the 775. However, for the

sealer to count these signals there must be transitions of the

signals within the range of 0.1 to 10 V, since this is the

input range over which the discriminator operates.

The flexibi l ity of the 775 makes it possible to count almost

any signal wider than 20 nsec and greater than 100 mV in

amplitude. There are two important points to remember

when supplying signals to the input: (1) The signal should

not cross the threshold level more than one time. Signals

with overshoot, ringing, etc., wil l be counted more than

once if the discriminator level is raised to the level at which

the perturbations occur. (2) Signals with slow rise and fall

times should be as clean (noise-free) as possible because of

the high gain and bandwidth of the 775 discriminator. As a

slow signal approaches the threshold, a smal l spurious noise

pulse can traverse the threshold and return, causing an extra

count to be added to the contents of the sealer.

Gate Input The Gate input signal can be connected to the

775 by either the front or rear panel BNC connector. As in