EG&G ORTEC 474 Betriebs- und Wartungshandbuch - Seite 8

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There are no typical control settings that can be sug

gested for operation, since each application of the 474

will require a different combination of functions. After

the system has been installed, use an oscilloscope to

observe the waveforms at the input and output of the 474

and adjust its controls to optimize its operation, con

sidering the functions that are required of it.

Generally speaking, the Integrate time constant can be

selected so that the risetime of the output pulses is nor

malized at a rate that is slower than the risetimes of the

input pulses. This function is of greatest value when the

pulses originate in a large detector so that they generate

a wide variety of risetimes and are difficult to observe for

timing measurements. The Differentiate time constant is

also selectable and determines the total interval before

the pulse returns to the baseline and allows a new pulse to

be observed. The combination of integration and differ

entiation time constants also contributes to the amount of

electronic noise that is seen in the system, so the resulting

waveforms should be considered from each of these

points of view and adjusted for optimum results.

When the shaping time constants impose considerable

changes in the input waveform, the nominal gain, which

is the product of the Coarse and Fine control settings,

may be degraded somewhat. This is not normally a pro

blem, since the gain is constant even though it may be less

than the nominal settings indicate.

CIRCUIT DESCRIPTION

The circuit of the ORTEC 474 Timing Filter Amplifier is

shown in schematic 474-0201-S1, included at the back of

this manual.

The front panel toggle switch, SI, selects a resistance

network for Invert or a circuit through Q.1 and Q2 for Non-

invert for pulses of either polarity, and the pulses are then

furnished into the differentiation network at 82. If 82 is

set at Out, the input pulse is coupled through R34 to the

input of A1. The pole-zero adjustment, R30, does not pro

vide any effect for the Out setting of 82. If 82 is set at any

of its other five positions, the input pulse is coupled

through a capacitor that is in parallel with a portion of the

signal, furnished through the pole-zero circuit, and pro

vided to the input of A1.

Amplifier A1 is an ORTEC Hybrid circuit, type HBA0106,

that includes Coarse Gain control 83. The amplified out

put at pin 5 of At is furnished to the integration network

at the input to A2, which is another type HBA0106 ORTEC

Hybrid circuit.

Amplifier A2 has a gain that is adjusted by Fine Gain con

trol R64. The output of A2 is furnished to the base of 09,

which is the input of the output voltage amplifier. The out

put voltage amplifier, consisting of transistors 09 through

Q20 and associated resistors and capacitors, has a volt

age gain of approximately 5. A complementary Darlington

output stage is used to provide good bipoiar drive capa

bility. Potentiometer R100 is a factory-adjusted balance

control for the two halves of the complementary Darling

ton output stage.

Integrated circuit 101 senses the output at CN2 and acts

in the dc feedback loop to force the output to zero. IC1 is

connected as an integrator, with a time constant of ap

proximately 150 IJ.S (corresponding to about 1 kHz).

The NIM power connector includes circuits that accept

±12 V and ±24 V. These input power levels are filtered and

are used internally in the circuits of the 474. The four

leveis are also furnished through the rear panel Preampli

fier Power connector, CN4, and can be used as the power

source for an associated ORTEC preamplifier.

MAINTENANCE

6.1.

CORRECTIVE MAINTENANCE

The ORTEC 474 should require no regular maintenance

other than replacement of components that have failed

due to age. Always ensure that the replacement compo

nents are equivalent to the original parts, designated in

schematic 474-0201-81. No internal trimming or adjust

ment is necessary for the 474.

To aid in the identification of a malfunctioning compo

nent, typical dc voltages are listed in Table 6.1. Note that

these are typical values, and may vary from one unit to

another without indicating a fault.

6.2.

FACTORY SERVICE

This instrument can be returned to the ORTEC factory

for service and repair at a nominal cost. The ORTEC

standard procedure for repair ensures the same quaiity

control and checkout that are used for a new instrument.

Always contact Customer 8ervices at ORTEC, (615) 482-

4411, before sending in an instrument for repair to obtain

shipping instructions and so that the required Return

Authorization Number can be assigned to the unit. This

number should be written on the address label and on the

package to ensure prompt attention when it reaches the

factory.