Operating Instructions
Chapter
3
3-1
3.1 Introduction
The Model 5184 Preamplifier can be powered from an external power source or from
internal alkaline cells as selected from a front-panel switch. In operation, the voltage to
be measured is connected to the AC-coupled INPUT BNC connector. The
preamplifier amplifies the signal voltage by a fixed 60 dB (1000 times) which is then
output from the OUTPUT BNC connector.
3.1.01 Power Switch
The three position POWER switch allows EXTERNAL, OFF, or BATTERY to be
selected. To operate the 5184 from an external power source, set the switch to the up
position. To operate the 5184 from internal batteries, set the switch to the down
position. In the center position, the 5184 is unpowered. The status of the selected
power source can be ascertained by pressing the POWER TEST button; the adjacent
LED will light if the power source voltage, whether of the external power source or the
5184 internal batteries, is above the minimum required value for reliable operation.
3.1.02 Input
The 5184 input circuit is of an asymmetrical differential configuration. When the
GROUND / ISOLATE switch is set to the down (GROUND) position, the screen of
the BNC input socket is grounded and the input may be used in the conventional
single-ended mode. When the GROUND / ISOLATE switch is set to the up
(ISOLATE) position, the input stage is floated and the input may be used in the
“pseudo-differential” mode. This gives the ground loop immunity normally associated
with differential inputs without the accompanying noise penalty associated with
differential input stages. In “pseudo-differential” mode the signal voltages should be
connected to the BNC INPUT socket and the signal ground to the GROUND terminal
on the front panel. The maximum common mode input voltage is 300 mV peak to peak
and the maximum voltage difference between the shell of the BNC signal input
connector and the front panel ground terminal is ±600 mV.
3.1.03 Output
The 5184 output can generate greater than 10 V peak to peak signals into loads greater
than 100 k
Ω
. The 450 ohm output impedance provides a convenient 10:1 output
attenuator if the amplifier is loaded with 50 ohms, which can be useful if the 5184 is
required to drive coax cable greater than one meter in length at signal frequencies
approaching 1 MHz.
