EG&G ORTEC 427 Gebruiksaanwijzing - Pagina 12

Blader online of download pdf Gebruiksaanwijzing voor {categorie_naam} EG&G ORTEC 427. EG&G ORTEC 427 20 pagina's. Delay amplifier

3-3

3.4

Linear Output Signal Connections and Terminating Impedance Considerations

The source impedance of the 0-10 volt standard linear outputs of most 400

Series modules is approximately 1 ohm. Interconnection of linear signals

is thus non-critical since the input impedance of circuits to be driven is

not important in determining the actual signal span, e.g., 0-10 volts, de

livered to the following circuit. Paralleling several loads on a single out

put is therefore permissible while preserving the 0-10 volt signal span.

Short lengths of interconnecting coaxial cable (up to approximately 4 feet)

need not be terminated. However, if a cable longer than qpRroxlniat&Ly

4 feet is necessary on a linear output, it shpuicL he, terminated in 0^^

load equal to the cable impedance. Since the output impedance is not

purely resistive and is slightly different for each individual module, when

a certain given length of coaxial cable is connected and is not terminated

in the"cKdfactefTsfic Impedance of the caBTe, oscillotions wilI generajjy^.

be observed

These os^^ at ions can be suppressed for any length of cable

by properly terminating the cable either in series at the sending end or in

shunt at the receiving end of the line. To properly terminate the cable at

the receiving end, it may be necessary to consider the input impedance of

the driven circuit, choosing an additional parallel resistor to make the com

bination produce the desired termination resistance. Series terminating the

cable at the sending end may be preferable in some cases where receiving

end terminating is not desirable or possible. When series terminating at

the sending end, full signal span, i.e., amplitude, is obtained at the

receiving end only when it is essentially unloaded or loaded with an im

pedance many times that of the cable. This may be accomplished by

inserting a series resistor equal to the characteristic impedance of the ca

ble internally in the module between the actual amplifier output on the

etched board and the output connector. It must be remembered that this

impedance is in series with the input impedance of the load being driven,

and in the case where the driven load is 900 ohms, a decrease in the signal

span of approximately 10% wil l occur for a 93-ohm transmission line. A

more serious loss occurs when the driven load is 93 ohms and the transmis

sion system is 93 ohms. In this case, a 50% loss will occur. BNC connec

tors with internal terminators are available from a number of connector

manufacturers in nominal values of 50, 100, and 1000 ohms. ORTEC stocks

in limited quantity both the 50 and 100 ohm BNC terminators. The BNC

terminators are quite convenient to use in conjunction with a BNC tee.