System for measuring contamination resistance

A test fixture is provided for testing the resistance associated with contamination material on the surface of electrical contacts mounted to a printed circuit board. A probe used to engage the contacts consists of first and second conductive probe segments which form a sandwich about a layer of insulating material. A current source provides a constant alternating current which is applied across the first and second probe segments. Circuitry is provided for amplifying the alternating current voltage developed across the first and second probe segments in response to the constant current. Circuitry is provided for rectifying the amplified alternating current voltage to provide a direct current voltage which is proportional to the measured resistance of the contact engaged by the probe. Data corresponding to the bulk and contact resistance associated with the clean contact is stored in memory of a computer. The bulk resistance represented by the stored data is subtracted from the measured resistance represented by the DC voltage of the contact under test in order to determine the contamination resistance.

BACKGROUND OF THE INVENTION 
This invention is directed to electronic apparatus for measuring the 
contamination resistance associated with electrical contacts contained on 
a printed circuit board. It more specifically addresses circuitry utilized 
in conjunction with a probe which engages the contacts in order to measure 
the contamination resistance. 
It is important that the contacts of a connector assembly associated with a 
printed circuit board do not exhibit excessive resistance to pins which 
will engage the contacts in order to minimize the attenuation of signals 
which will pass through the contact/pin coupling. Contamination resistance 
is the resistance associated with a film or layer of material on the 
contact which separates an inserted pin from the base metal or the plated 
surface of the contact. The total resistance associated with a pin 
inserted in a contact includes the resistances of the pin and contact 
materials, the contact resistance between the pin and the contact, and the 
contamination resistance. Contact resistance is the resistance that would 
normally be present at the physical area of contact between a clean pin 
and a clean contact. 
It is desirable to be able to measure the contamination resistance 
associated with printed circuit board contacts in order to insure that 
excessive resistance will not be presented when the board is installed. 
Excessive resistance will result in attenuated signals or discontinuities 
in which the signal will not be coupled at all. Difficulties have been 
encountered in attempting to make resistance contamination measurements 
which are repeatable due to the low resistance values normally associated 
with such measurements. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an improved apparatus 
for making accurate and repeatable contamination resistance measurements. 
In accordance with an embodiment of the present invention, an electronic 
apparatus is provided for measuring contamination resistance including a 
probe which includes first and second conductive probe segments that form 
a sandwich about an insulating layer. A constant current source of 
alternating current is applied across the first and second probe segments 
to generate an AC voltage which is amplified and rectified thereby 
resulting in a DC voltage proportional to the measured resistance between 
an engaged contact of a contact and the probe. A computer includes a 
mechanism for converting the DC voltage into a digital value representing 
the measured resistance value. The computer includes previously stored 
data corresponding to the bulk resistance associated with the engagement 
of the probe and a clean contact. The contamination resistance is obtained 
by subtracting the bulk resistance stored in memory from the value of 
resistance determined by the resistance measurement. The result from the 
subtraction process is displayed on a monitor of the computer and analyzed 
to facilitate a determination of whether the contamination resistance is 
within an acceptable range.

DETAILED DESCRIPTION 
The purpose of the system as shown in FIG. 1 is to measure the 
contamination resistance associated with the contacts (connectors) in 
connector assembly 22 of printed circuit board (PCB) 20. Contamination 
resistance is the electrical resistance caused by various types of 
contamination films and materials which may become disposed on the 
electrical contacts in assembly 22. Such contamination may result from the 
soldering or cleaning operations associated with PCB 20 or other 
manufacturing operations. Excessive resistance exhibited between 
electrical pins which will be received in the female contacts of assembly 
22 may lead to a higher than expected resistance connection of signals 
flowing between the respective jack and female contact, or may lead to an 
intermittent connection due to the contamination between the jack and the 
contact. The illustrative system measures the contamination resistance 
associated with the contacts in assembly 22 as a quality assurance. This 
testing includes the insertion of conductive probes associated with probe 
assembly 46 into at least a sampling of the contacts of assembly 22 and 
calculating the contamination resistance associated with such 
measurements. 
FIG. 1 illustrates an embodiment of a system in accordance with the present 
invention for making contact contamination resistance measurements. A 
resistance measuring device 10 operates under the control of a personal 
computer 12 which is coupled to device 10 by communication lines 14 and 
16. The resistance measuring device 10 also receives conventional AC power 
by power line 18. A printed circuit board (PCB) 20 includes a connector 
assembly 22 including a plurality of female contacts (not seen in FIG. 1; 
see FIGS. 4 and 6). The connector assembly 22 is seated within a 
longitudinal channel 26 disposed in a front structural element 28 of 
device 10. The contacts of assembly 22 are accessible from the bottom of 
structure 28 for probing. A fixed edge holder 30 provides a stop for the 
right edge of PCB 20 as shown in FIG. 1. A movable edge holder 32 engages 
the left edge of the PCB 20 and can be moved laterally to accept different 
widths of printed circuit boards since it is mounted to a movable slide 34 
which can be slid within channel 26. A plurality of air-operated solenoids 
(cylinders) 36 are disposed in spaced-apart relationship along channel 26 
so that the cylinder rods (arms) 38 (not seen in FIG. 1; see FIG. 6) can 
be extended so as to engage connector assembly 22 to securely hold the 
connector assembly within channel 26. 
The device 10 includes motors 40, 42, and 44 which are utilized to control 
the position of probe assembly 46 in the X, Y, and Z axes, respectively. 
The motors are operated under the control of PC 12. Movement control 
assemblies 50, and 52 have their positions controlled by motors 40, 42, 
and 44, respectively, thereby controlling the position of the probe 
assembly 46 in the X, Y, and Z axes, respectively. Assembly 48 moves along 
the X axis as supported by guide rods 54 and is controlled by threaded rod 
56 as driven by motor 40. Similarly, assemblies 50 and 52 are guided for 
support in the Y and Z axes as controlled by motors 42 and 44, 
respectively. It will be well known to those skilled in the art that a 
variety of techniques exist for providing three-dimensional control of a 
sensor or object. Since a variety of mechanisms and assemblies can be 
utilized to accomplish the three-dimensional control of the probe assembly 
46, specific structural details and operation of these mechanisms are not 
described. 
FIG. 2 more specifically illustrates the mechanisms 48, 50, and 52 utilized 
to control the position of the probe assembly 46 relative to the contacts 
in connector assembly 22. Limit switch assemblies 60 and 62 provide 
over-travel and zero reference (home) position feed back used by the 
computer 12 and carried by cables 60A and 62A, respectively. Motor drive 
cables 42A and 44A control power to motors 42 and 44, respectively, as 
determined by computer 12. Similarly, as best seen in FIG. 1, limit switch 
assembly 41 provides control signals carried by cable 41A to computer 12, 
and motor drive cable 40A controls the power to motor 40 under the control 
of computer 12. Each limit switch assembly may contain near and far over 
travel switches and a home switch that establishes a reference position 
for the corresponding axis. Cable 14 carries the signals associated with 
cables 40A, 41A, 42A, 44A, 60A, and 62A. 
A single printed circuit board 64 is mounted to assembly 52 and contains 
circuitry associated with the making of the resistance measurements in 
conjunction with the probe assembly 46. The circuitry and probe assembly 
are described below. A plurality of wires 66 coupled to the circuitry on 
PCB 64 are coupled to PC 12 via cable 16 as shown in FIG. 1. The control 
signal conductors associated with cables 60 and 62, as well as the cable 
associated with the control of motor 40, are coupled to PC 12 via cable 14 
as shown in FIG. 1. Once the probes in the probe assembly 46 are aligned 
in the X and Y axes with connectors in the connector assembly (see FIG. 
4), the motor 44 controlling the Z axis moves the probe assembly upward 
along the Z axis to engage the connectors. After a resistance measurement 
has been taken, motor 44 causes assembly 52 including probe assembly 46 to 
move downward in the Z direction to disengage the connector following the 
measurement. 
Referring to FIGS. 3 and 4, the probe assembly 46 includes a main bracket 
or housing 70 which is mounted to assembly 52. In the illustrative 
embodiment, probes 72 and 74 are spaced apart in the X axis and offset in 
the Y axis so as to concurrently engage contacts 76 and 78 in the 
connector assembly 22 when the probe assembly 46 is moved upward in the Z 
direction during a measurement. The spacing in the X axis is consistent 
with the spacing in the X axis between contacts. The offset or spacing in 
the Y axis equals the center-to-center spacing in the Y direction between 
the two rows of contacts. This allows two different contacts (one in each 
of two rows) to be measured during one upward movement in the Z direction 
of probe assembly 46. The probes 72 and 74 as well as their supporting 
structure are identical, and hence only the supporting structure relating 
to probe 72 will be described. 
Probe 72 is mounted to a bracket 80 by an insulating sleeve 82. A tubular 
collar portion 84 of sleeve 82 receives a hollow tube 86 about which a 
helical spring 88 is wrapped. A stop (not shown) in collar 84 engages rod 
86 and spring 88. A hollow threaded sleeve 90 engages a threaded hole 92 
in a support bracket 93 so as to permit the passage of tube 86 while 
providing a stop for the other end of spring 88. The nut 90 is adjusted to 
provide a predetermined bias force in the Z direction for probe 72. Two 
pairs of wires 94 and 96 connected to probe 72 pass through the hollow 
tube 86. As will be discussed in detail below, each of the pairs of wires 
94 and 96 are attached to respective first and second probe segments which 
constitute the probe 72. 
Probe holding bracket 80 is mounted to a mechanism 100 which maintains 
probe 72 in a precisely perpendicular alignment to the X and Y planes 
while permitting substantially unimpeded movement of probe 72 along the Z 
axis. In the illustrative embodiment of the present invention, the 
mechanism 100 is a ball slide device. This device includes an element 102 
which is free to move relative to element 104 in the Z direction as shown 
in FIG. 4 as guided by ball bearings 106 which operate within a race 108. 
The bearing and race arrangement disposed between elements 102 and 104 
define a precise controlled linear movement in only a single direction. 
FIG. 4 shows spring 88 urging the sliding element 102 against a stop 
portion of bracket 70. 
In preparation for making a resistance measurement, assembly 52 is driven 
upward in the Z axis by motor 44 by a distance sufficient to cause probe 
72 to engage the contact 76 thereby stopping the vertical motion of the 
probe 72. This causes spring 88 to be compressed. In the illustrative 
embodiment the force applied by spring 88 is insufficient to overcome the 
resistance of the leaves of contact 76. Element 104 of the ball slide 100 
is fixedly mounted to bracket 70 restricting the movement of probe 72 to 
movement only in the Z axis. 
FIG. 5 is an enlarged view illustrating the engagement of probe 72 and 
contact 76. As illustrated, contact 76 has a downward flair such that 
increasing mechanical resistance is applied to a pin inserted when the PCB 
is mounted for operation. The force provided by spring 88 urges the probe 
72 into engagement with the contact but is not sufficient to cause 
substantial spreading of the leaves of the contact. This results in only 
the distal end of the probe abutting the contact. Probe 72 is preferably 
gold plated and consists of a first probe segment 72A and a second probe 
segment 72B which are separated by a layer of insulating material 72C so 
as to comprise a sandwich of separated conductive probes. The distal end 
of the probe 72 is preferably rounded like a dome. A constant current 
source of alternating current (AC) is connected across probe segments 72A 
and 72B by wires 94. This results in an induced AC voltage drop which is 
coupled by wires 96 to sensing circuitry which will be described below. By 
generating an AC current of predetermined magnitude which is connected 
across or in parallel with probe segments 72A and 72B, the magnitude of 
the AC voltage drop will be proportional to the resistance across the 
probe segments 72A and 72B. 
The total sensed resistance by this measurement can be conceptualized as 
represented by three series resistances: bulk resistance of the probe 
segments and the contact under test; contact resistance which would be 
present between a clean contact and clean probe segments 72A and 72B; and 
contamination resistance typically due to a film of contamination material 
existing between the surfaces of the contact and the areas of probe 
segments 72A and 72B which engage the contact. In accordance with a 
preferred embodiment of the invention, data representing previous 
resistance measurements made between clean probes and clean contacts are 
recorded and stored in PC 12. This data represents the combined bulk and 
contact resistance. The contamination resistance can be determined by 
subtracting these predetermined resistances from a measurement made of 
contacts of unknown contamination levels. 
Referring to FIG. 6 and FIG. 4, a plurality of air-driven solenoids 36A-36E 
are spaced apart and aligned so that their respective cylinder rods (arms) 
38A-38E will engage the side of connector assembly 22 if the connector 
assembly is opposite a respective cylinder. If the connector assembly is 
of a length such that some of the cylinder rods of the cylinders will not 
engage the connector assembly, the cylinder rods of such cylinders will 
proceed to extend further forward as indicated by cylinder rods 38D and 
38E. Each of the cylinders is driven by a cable connected to a supply of 
air at an appropriate pressure to cause a desired force to be exerted by 
the respective cylinder rods on connector assembly 22. The force provided 
by the extended cylinder rods engaging connector assembly 22 securely 
holds the connector assembly in place in the channel 26 and prevents 
movement of the connector assembly as the probes engage the contacts of 
the assembly. An electrically controlled air valve (not shown) operates 
under the control of PC 12 so as to simultaneously supply or not supply 
air to the solenoids. It will be apparent to those skilled in the art that 
other types of solenoids driven by other types of force could be utilized 
to provide the desired action of clamping or captivating the connector 
assembly 22 securely to member 28. 
Switches 122-130 are associated with solenoids 136A-136E, respectively, and 
are designed to provide an indication of whether the respective cylinder 
rods of the solenoids have extended beyond a predetermined travel. In the 
illustrative example, the solenoids are placed at a distance relative to 
channel 26 and the connector assembly 22 such that the switches remain in 
an open position if the cylinder rods engage the connector assembly but 
will close to provide continuity if the cylinder rods travel further as is 
the case with cylinder rods 38D and 38E. Thus, switches 128 and 130 are 
closed while the remaining switches 122, 124, and 126 are open providing 
signals on wires 132-140 to PC 12 indicative of whether the cylinders have 
engaged the connector assembly or not. These wires are part of the signals 
coupled to PC 12 via cable 16. Since the purpose of the device 10 is to 
permit the testing of printed circuit boards and connector assemblies of 
different lengths, this provides an indication of the length of connector 
assembly disposed for test in device 10. Since the resistance test program 
may vary for different connector assemblies and lengths of connector 
assemblies, the signals carried by wires 132-140 provide feedback signals 
which are monitored by a routine in the control program of PC 12 to 
determine if the actual printed circuit board 20 and its corresponding 
connector assembly 22 inserted for test in device 10 is consistent with 
the type of test selected by an operator of the system. 
For example, it may be desirable to test a predetermined percentage of the 
number of contacts in a connector assembly to insure statistical 
significance. Thus, for a longer connector assembly with a larger number 
of contacts, more of the contacts will need to be probed and resistance 
measurements taken in order to satisfy the desired criteria. A user may 
select different programs which correspond to the different number of 
tests and contacts to be tested. The feedback signals provided by wires 
132-140 provide the program with information which can be used to confirm 
that the number of contacts selected to be tested by a given test program 
exist, i.e. that a printed circuit board of the type selected for testing 
has actually been inserted into device 10. The use of solenoids which have 
integrated capabilities for providing an indication of the amount of 
travel of their respective cylinder rods provides the dual function of 
holding the connector assembly in place and providing feedback signals 
indicative of the length of the actual connector assembly in device 10. 
FIG. 7 illustrates a schematic diagram of circuitry in accordance with the 
present invention. The upper portion of the circuitry shown in FIG. 7 is 
utilized to provide a constant current source of AC current of 
predetermined magnitude to probe 72 by wires 94. The bottom portion of the 
circuitry senses the voltage developed across probe segments 72A and 72B 
as induced by the constant current, amplifies the sensed AC voltage 
delivered by wire 76, rectifies the AC voltage to provide a DC voltage, 
and provides a buffered output of the DC voltage to output channel 150 
which is coupled to PC 12 as part of the measurement system cable 16. 
The constant current producing circuitry includes an integrated circuit 
IC1, which may comprise a 555 timer which is used to generate a square 
wave signal which is scaled and filtered by components R1, C1, and R2. An 
enable line 152 controls transistors Q1 and Q2 to determine whether the 
square wave from IC1 is delivered to amplifier IC2. A low or ground signal 
on enable line 152 causes transistor Q1 and Q2 to conduct and causes Q2 to 
reflect a low impedance to ground path at the input to IC2 thereby 
substantially attenuating the signal. The NPN transistor Q2 is used in an 
inverted configuration (the functions of the collector and emitter are 
reversed, i.e. collector to ground, and emitter to the input to be 
shunted) to provide a very low saturation voltage. In accordance with an 
embodiment of the present invention, the illustrative circuitry in FIG. 7, 
except for the basic generator of IC1, is duplicated for the other probe 
74. Thus, the enable line is utilized to selectively enable the particular 
circuitry associated with the probe which is making a measurement. 
Preferably, both probes are not activated for measurement simultaneously 
in order to minimize the possibility of "cross talk" which could cause one 
circuit to interfere with the measurement being made by the other 
circuitry. Cross talk is further minimized by the isolation provided by 
transformer T1. Another advantage of the isolation of transformer T1 is 
that interconnections on the PCB 20 between the contacts do not interfere 
with the contamination resistance measurements. Diodes D1, D2, D3 and D4 
limit the voltage that can be generated across the primary of transformer 
T1 and hence limit the current source to producing about 40 millivolts at 
the transformer's secondary if an open circuit load (no load to probe) is 
encountered. This is designed to prevent break down of a thin layer of 
contamination on the contact being measured due to too high a voltage. If 
a break down were to occur, a thin layer of contamination would likely go 
undetected due the lowered resistance that would result from the break 
down. 
Integrated circuit IC2 is utilized to convert the input AC voltage from IC1 
to a regulated AC current driving the primary of transformer T1. The 
secondary of transformer T1 is coupled to wires 94 to provide a constant 
current source of AC current such as at 100 milliamperes. Relay K1 which 
operates under the control of PC 12 can be activated to cause it to place 
a precision resistor R3 across the secondary output of transformer T1 to 
provide a calibration standard of known resistance for the resistance 
measurement system. This calibration is conducted with the probe not 
engaging a contact so that a resulting DC voltage present at output 150 
for a known resistance across probe segments 72A and 72B can be 
determined. Relay K1 is illustrated in the inactivated or normal operating 
state in which resistor R3 is not placed in parallel with the secondary of 
transformer T1. 
The AC voltage developed by the AC current will be proportional to the 
resistance across probe segments 72A and 72B. This voltage is amplified 
with band pass filtering provided by amplifiers IC3 and IC4 and the 
accompanying associated circuitry. Integrated circuit IC5 in combination 
with diode D5 serves to rectify the AC voltage and provides a DC voltage 
as an input to buffer IC6 which provides a unity gain buffering function 
to drive line 150 with the DC voltage. It will be apparent to those 
skilled in the art that the DC output voltage on line 150 will be 
proportional to the resistance across probe 72 in accordance with Ohms 
law. 
FIG. 8 illustrates a block diagram of personal computer 12 which includes a 
microprocessor 160 which is supported by read-only memory (ROM) 162, 
random access memory (RAM) 164 and a nonvolatile storage device such as a 
hard disk drive 166. User inputs are provided to the microprocessor by 
keyboard 168; outputs visual and audible are provided by monitor 170. An 
input/output interface device 172 provides an interface between 
microprocessor 160 and the signals received from and sent to resistance 
measuring device 10 via communication lines 14. The input/output interface 
device 172 preferably includes a commercially available three axis motor 
controller I/O board for controlling the X, Y, and Z motors. Such a motor 
controller board accepts movement commands from microprocessor 160 and 
generates appropriate enable, step, and direction signals for each motor 
as well as controlling the proper sequence of operation of the motors. 
This board monitors and responds to the status of the home and limit 
switches associated with each motor. An analog-to-digital converter 174 
converts the received DC voltages indicative of the measured resistance 
into digital data having a corresponding value. The DC voltages are 
carried by channel 16 and lines 150 for probes 72 and 74. This digital 
data is processed by microprocessor 160 in order to derive the resistance 
associated with contamination of the contact upon which the resistance 
measurement was made. The microprocessor operates under the control of 
program instructions such as stored in ROM 162 and disk drive 166 to 
process the measurements and to control the operation of resistance device 
10. 
An example of operation of the illustrative contamination resistance 
measuring system is provided in the following table. 
TABLE 
1. The user selects the specific PCB/connector assembly to be tested from a 
table of selections provided as a menu on the monitor of the PC. 
2. The user then inserts the corresponding PCB into the test fixture and 
enters the appropriate start command from the keyboard of the PC. 
3. The PC sends signals to the test fixture causing the solenoids to 
activate, i.e. causing their cylinder rods to be extended to engage and 
clamp the connector assembly 22 in place. The PC then checks the state of 
the switches associated with the solenoids against a stored table of 
correct states for the selected test program. If the sensed switch 
conditions do not match with the table, an error condition exists and a 
message is displayed on the PC monitor advising the user to check for the 
insertion of the proper PCB and to check the selection of a proper test 
program. Assuming that the switch states match with the anticipated switch 
states stored in the table associated with the selected test program, the 
test proceeds. 
4. A self calibration test is initiated by the PC sending a signal causing 
relay K1 to change from the normal test position (as shown in FIG. 7) to 
the calibrate position, thereby placing the calibration resistance in 
parallel across the first probe presenting its Kelvin connections to the 
measurement system. The PC then sends an enable signal via line 152 
activating the circuitry associated with the first probe. The developed DC 
voltage is output on lines 150 and 16, and converted into digital data at 
the PC. This voltage represents the measured resistance of a known 
resistor, e.g. 100 milliohms. The PC calculates a calibration factor which 
is the ratio of the actual resistance to the measured voltage. This 
calibration factor accounts for all the system gains (including the 
current source and sensing circuitry). The calibration factor is stored in 
memory. During actual measurements of contact resistance, the measured 
voltage is multiplied by the calibration factor to determine the unknown 
resistance of the contact under test. 
5. The program homes the probe assembly to a reference X, Y, Z position and 
then proceeds to locate a table of stored data to determine the 
corresponding X, Y, Z test positions of the probe assembly for the 
selected test program. A first X, Y, Z location is selected. 
6. The PC sends a sequence of command signals controlling the X, Y, Z 
motors which cause the probe assembly to move into the appropriate X, Y 
position and then engage a first set of contacts by moving upward in the Z 
direction. 
7. The PC sends an enable signal causing the first probe measuring 
circuitry to be enabled. A first resistance measurement is made and the 
corresponding digital value stored. This measured value is adjusted by 
multiplying it by the calibration factor stored in memory. 
8. While still in the same X, Y, Z position, the PC preferably sends a 
signal disabling the circuitry associated with the first probe and sends 
an enable signal to enable the circuitry associated with the second probe. 
The resistance measured with the second probe is stored in the PC as a 
digital value and adjusted by the calibration factor. 
9. The PC then proceeds to calculate the contamination resistances 
associated with each stored digital data value representing a measured and 
adjusted resistance. This calculation consists of subtracting a 
predetermined bulk resistance value, representing the probe resistance and 
the normal surface resistivity associated with a clean contact and probe, 
from each measured value to obtain the contamination resistance. The bulk 
resistance of each probe is predetermined and stored in memory during a 
probe characterization procedure performed periodically. 
10. The program compares each calculated contamination resistance for each 
probe to a predetermined acceptance range of contamination resistances 
stored for the corresponding PCB. A first time pass/fail determination is 
made for the two contacts measured. If either measured resistance fails 
the test, i.e. is outside the acceptance range, the probe assemblies are 
lowered in the Z axis to disengage the contacts, raised again to re-engage 
the same contacts, and the measurements made again. A failure is 
determined if the second measurement of a contact is also outside the 
acceptance range. The PC displays the measured contamination resistances; 
resistances which are not within the acceptable range are marked with a 
flag for easy visual identification. Two successive fail measurements for 
a contact are required in the illustrative embodiment for a failure to be 
determined. For example, a failing measurement of a contact on the first 
try followed by a passing measurement on the second try would be 
considered a "pass". This process is repeated until all contacts to be 
tested have been measured and values stored in memory. 
11. The calculated contamination resistance values are displayed on the 
monitor of the PC as a two column table where each column shows the 
resistances associated with the measurements for the first and second 
probes, respectively. The PC also displays an overall board pass/fail 
indication based on exceeding a predetermined number of contact resistance 
failures associated with each board. 
12. The data associated with the resistance measurements of a PCB are 
preferably stored in the PC's memory and utilized for statistical 
determinations associated with quality control and process monitoring. 
13. Following the completion of the testing of all contact locations for 
the selected PCB, the probe is returned to a "home" X, Y, Z location. 
Although an embodiment of the invention has been described and illustrated 
in the drawings, the scope of the invention is defined by the claims which 
follow.