FIELD OF THE INVENTION
The present invention relates to a device used for linear measurements more
particularly it relates to measuring the center-to-center distance of grooves in
the oil field equipment.
BACKGROUND OF THE INVENTION
Oil field equipment components for example, tubing spool, full four valve easing
head and other components having ring joint gasket grooves on the face in
which metallic gasket are used for sealing flange connections. These grooves are
with V-shape with included angle of 46 deg with controlled dimensions as shown
in Figure 1. For measuring the center of groove, prior art use a center measuring
vernier. It is difficult to measure the center distance with conventional vernier.
The measurement of inner to outer groove dimensions and thereby calculating
the center distance of the groove provides an inaccurate data resulting in
improper seating of the gaskets on the grooves leading to imperfect sealing of
the flange connection. Hence, there is a need for a technique to accurately
measure the center distance of the groove directly as well as accurately for
perfect seating of the gaskets to provide a leak proof flange connection.

JP 5540604 entitled THE TAPERED SEAT SURFACE OF THE MEASURING
METHOD AND A MEASURING DEVICE", provides a measuring device of a
tapered seating face capable of precisely measuring a tapered seating face.
According to this prior art, the measuring device of the tapered seating face
includes a head section inserted into a seating face having a tapered surface and
at least two gap sensors that are provided on the surface of the head section in
a depth direction of the seating face and measure the amount of gap from a
predetermined reference point (head section surface) to the seating face.
JP 2008249408A2008 entitled "METHOD AND DEVICE FOR MEASURING GROOVE
OF BEARING', proposes a bearing groove measuring method capable of
enhancing measurement precision of the dimensions of the grooves of bearing.
According to this invention, the method comprises arranging a plurality of
spherical substances between guide grooves formed in the inner circumference
of the outer member of the bearing and an inclined surface formed on the
circumference surface of the measuring shaft; rotating the outer member with
respect to the measuring shaft along with imparting a predetermined load in a
direction of inserting the measuring shaft into the outer member; measuring a
relative axial position to one of the outer member and the measuring shaft of the
other, calculating from those axial positions their average value; and calculating
diameter dimensions of the guide grooves on the basis of the average value.

However, the prior patents are used in the measurement of grooves but the
methods is are different.
OBJECT OF THE INVENTION
It is therefore an object of the invention to propose an apparatus for accurately
measuring the center to center groove distance of oil field components.
A still another object of the invention is to propose an apparatus for accurately
measuring the center to center groove distance of oil field components which
directly arrives to the measured results without any manual calculation.
SUMMARY OF THE INVENTION
According to the invention, the measuring apparatus is having a known linear
measuring vernier in which two probe holders are fastened respectively to a
fixed jaw and a movable jaw. The said probe holders each having a face hole for
clamping on the respective jaws. The probe holders are tightened by pins. The
probes perfectly machined according to the included angle of the grooves are
inserted in the holes provided in the probe holders. By this arrangement, the
probes are secured tightly in the vernier caliper for direct measurement of the
center distance of the grooves in the oil field components which avoids the
limitations of the prior art.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 shows the object with grooves which is to be measured.
Figure 2 shows the apparatus with attachment for the measurement.
DETAIL DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
As shown in Figure 2, the groove measuring apparatus (01) is connected by two
probe holders (02 and 03) on the respective fixed movable jaw. The probe
holders (02, 03) having face holes for clamping with pins (05). The first probe
(04) is connected to the fixed jaw by inserting in the tapered hole provided in
the probe holder. In the same way, the second probe (04) is connected to the
moveable jaw. Because of this arrangement, the linear distance up to 600 mm
between the center of the grooves in the oil field components can be measured
directly without any additional calculation and overcoming the drawbacks of the
prior art. The probes are replaceable with different sizes for different shape of
grooves.

WE CLAIM :
1. An apparatus for accurately measuring the centre to centre groove
distance of oil field components, without calculation of errors
comprising:
two probe holders (02 and 03) with holes provided respectively on a
movable jaw and a fixed jaw of a known linear measuring vernier (01);
the probe holders are connected by at least a couple of pins (05) to the
fixed and movable jaws;
two probes are machined corresponding to the dimensions of the
groove of the component, and having at least a couple of pins at the
top and external thread;
the probes (04) are screwed into the tapered hole of the probe holder
(02, 03) and secured by screws (06) in the fixed jaw.
2. The apparatus as claimed in claim 1, wherein the jaw with fixed
probes (04) are positioned in the grooves of the work piece, and

the center to center distance of the groove is measured precisely
without any further calculation.