Electricity: measuring and testing – Testing potential in specific environment – Voltage probe
Reexamination Certificate
2000-06-29
2002-10-15
Lefkowitz, Edward (Department: 2862)
Electricity: measuring and testing
Testing potential in specific environment
Voltage probe
C324S149000
Reexamination Certificate
active
06466000
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to measurement probes and more specifically to a replaceable probe tip holder for a wide bandwidth, high frequency measurement probe, such as used with measurement test equipment like oscilloscopes, logic analyzers and the like.
A typical measurement probe is described in U.S. Pat. No. 5,061,892 for acquiring electrical signals from a device under test in the megahertz range. The probe has probe head with an electrically conductive hollow tube having a substrate disposed therein. The substrate has passive and/or active circuitry to prevent loading of the test device. The end of the hollow tube has an insulating plug disposed therein with a coaxially disposed probing tip extending out of the plug in both directions. The portion of the probing tip extending into the hollow body is electrically connected to the substrate by a spring loaded electrical contact electrically connected to the substrate. A damaged or broken probe tip may be replaced by replacing the plug and associated probe tip. One drawback to this type of probe design is limited bandwidth of the probe caused by the capacitance of the probe tip and the spring loaded electrical contact. At high frequencies, measures need to be taken to minimize the probe tip capacitance.
High frequency measurement probes, such as for probing signals in the 3 Ghz to 4 Ghz range, require high input resistance values and low input capacitances. Generally, these types of probes have an active FET input for low circuit loading and have a frequency bandwidth up to 4 Ghz or more. An example of such a probe is the P6217 Active FET Probe, manufactured and sold by Tektronix, Inc., Beaverton, Oreg. and assignee of the instant application.
FIG. 1
is a cross-sectional view of the P6217 probe
10
showing the internal configuration of the probe elements. The probe
10
has an electrically conductive circular tubular housing
12
in which is disposed a substrate
14
. The substrate is slightly off center in the tubular housing so that the upper surface of the substrate is centered in the housing. The end of the substrate
14
is tapered to provide clearance for a probe tip holder
16
and extends slightly outward from the end of the tubular housing approximately 0.025 inches. Passive and active electrical components
18
, such as FET transistors, resistors, capacitors and the like are mounted on the substrate. A gold foil contact
20
extends over the front end of the substrate
14
for providing an electrical connection between the substrate
14
and a probing tip
22
. The probe tip holder
16
is made of insulating material, such as plastic or the like, is secured within the end of the housing
12
. The holder
16
has a cavity
24
with a tapered end
26
that receives a portion of the substrate
14
extending out past the end of the housing
12
. The tapered end
26
is centrally formed in the holder
16
and has a bore
28
extending therefrom to the front end of the holder
16
. The probing tip
22
has a head
30
and a shank
32
that is disposed in the holder
22
with the head
30
positioned in the tapered end
26
and the shank
32
extending through the bore
28
with the tip of the shank
32
exposed at the front end of the holder
16
. A resilient elastomeric member
34
is disposed in the tapered end
26
between the probing tip head
30
and the holder to provide a compressive force between the head
30
and the gold foil contact
20
on the end of the substrate
14
. An insulating boot
36
is positioned over a substantial portion of the tubular housing
12
to electrically insulate the housing
12
from the user.
A major drawback to the probe shown in
FIG. 1
is that the probing tip
22
is not replaceable.
FIG. 2
shows the structure of the holder
16
that is secured into the tubular housing
12
. The holder
16
has an outer flange
38
that abuts against the tubular housing
12
when the holder
16
is inserted into the housing. Extending from the flange
38
is a circular support member
40
that is received in the tubular housing
12
. Because of the position of the substrate
14
within the housing
12
, the lower portion of the support member
40
is removed to provide clearance for the holder
16
. To allow the holder
16
to be inserted into the housing
12
in two positions, the upper portion of the support member
40
is also is also removed. This weakens the support member
40
. To increase the strength of the support member
40
, the rounded inner surfaces are thickened to produce opposing approximate half-mooned shaped support members
42
having parallel surfaces
44
. The resulting shape of the support member
40
requires precise alignment of the holder
16
in the tubular housing
12
. The parallel surfaces
44
need to be positioned perpendicular to the top surface of the substrate
14
. Positioning the parallel surface
44
in a non-vertical position causes the support member
40
to hit the substrate
14
causing irreparable damage. Precisely aligning the holder
16
in the tubular housing
12
requires the use of a microscope and special fixturing that is not available to a user. Not being able to replace broken probing tips on such probes becomes expensive for customers with such probes costing in the $3,000 range.
What is needed is a replaceable probe tip holder and an associated probe head for a measurement probe. The probe tip holder should be easily replaceable without a need for special tools, fixturing or microscopes. The holder and associated probe head configuration should minimize the probe tip capacitance to provide a wide bandwidth, high frequency measurement probe.
SUMMARY OF THE INVENTION
Accordingly, the present invention is a replaceable probe tip holder for a measurement probe head. The probe tip holder includes a cap and attachment arms extending from the back end of the cap that are positionable on the outside of a tubular housing of the probe head. The back end of the cap has a first cavity formed therein that is sized to receive a portion of the front end of the tubular housing. A second cavity extends from the first cavity and is sized to receive a portion of a substrate that extends beyond the front end of the housing. At least a first bore is formed in the cap from the second cavity to the front end of the cap. Each attachment arm may include a latching member in the form of a protrusion or an aperture. The protrusions are formed on inward facing surfaces of the attachment arms and are circular in form with each protrusion having an angled surface extending from the surface of the attachment arm to a top surface of the protrusion. The probe tip holder may also be configured with a second bore formed from the second cavity to the front end of the cap and disposed adjacent to the first bore. At least a first probe tip cavity may also be formed in the cap extending from the second cavity and sized to receive a first resilient compression member with the first bore formed from the probe tip cavity to the front end of the cap. A second probe tip cavity may also be formed in the cap that is disposed adjacent to the first probe tip cavity and extends from the second cavity with a second bore formed from the second probe tip cavity to the front end of the cap. The probe tip cavity is sized to receive a second resilient compression member. In the preferred embodiment of the present invention the center to center separation of the first and second bores is in the range of 0.100 inches. The depth of the first cavity in the range of 0.165 inches and the depth of the second cavity is in the range of 0.100 inches. The resilient compression member is preferably a nonconductive elastomer. A first electrically conductive probe tip having a shank and a head with the shank is positioned within the cap such that the head is in contact with the first resilient compression member and the shank extends through the first bore with the end of the shank extending from the front end of the cap. A second electrically conductive probe tip co
Bucher William K.
Lefkowitz Edward
Tektronix Inc.
Zaveri Subhash
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