Tektronix P7313SMA, Техническое описание

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Operating Basics
In Ext mode, the external DC voltage is connected to the red (+) and black (-) terminals on the end of the probe head, which
accept standard 80 mm plugs. A pair of 0.080 in-to-banana plug adapter cables are included with the probe for making
connections from these connectors to external power sources. The black terminal is ground and is connected to the outer
case of the shielded module that holds the SMA input terminals. When you are not using these terminals, they can be left
open and unconnected. When the Ext mode input terminals are left open, the Ext mode termination voltage defaults to 0.0 V.
The termination voltage supplied to the input termination network by the Vterm driver can be monitored with a DMM on a
pair of 0.040 inch pin jacks on the top of the probe. This allows you to verify the termination voltage setting, and when you
are using Auto mode, allows you to measure the common-mode input voltage.
You can use a pair of 0.040 inch-to-0.080 inch pin jack adapters with the 0.080 inch-to-banana plug cables (both are standard
accessories included with your probe), to make a more permanent connection to the monitoring DMM.
Overdrive Error
The P7313SMA differential probe can measure signals that have a common-mode voltage range of ±2.5 V. Although the
termination voltage range is speci
fi ed to be +3.6 V/–2.5 V, limitations on the linear current range of the termination voltage
driver restrict the voltage difference between V
CM
and V
T
.
Generally, you must keep the termination voltage within about 2 volts of the common-mode voltage (when using a supply
with 0
Ω source impedance), or 3 volts of the common-mode voltage (with a 50 Ω source impedance), or the Overdrive Error
LED will glow solid, indicating an over-current situation, which may lead to a measurement error.
The speci fi c voltage difference between V
CM
and V
T
is dependent on both the source impedance and the V
CM
and V
T
values. You can use the input termination network table to determine allowable conditions, with the Overdrive Error current
threshold for I
T
set at about ±80 mA. (See Table 1 on page 4.)
The Overdrive Error LED will also fl ash red when the termination voltage exceeds the all3.6 V/–2.5 volt range. This
can occur in Auto mode when V
CM
exceeds a threshold of about ±2.8 V, or in Ext mode when the V
T
input voltage exceeds
the same threshold. If this occurs, remove all signal sources from the probe to clear this LED.
The Overdrive Error LED provides an active status monitor of error conditions; it does not latch and store the occurrence of
an error condition.
Figure 6: Overdrive Error indicator
10 P7313SMA Technical Reference