Remote transducer monitoring system

A transducer monitoring system facilitating at least two measurements in locations which are difficult to access. Advantages include the capability of making the measurements in remote locations where severe environmental conditions exist. A feature of the invention is in its implementation at these remote locations without requiring additional conductors over the requirements for one-parameter measurements. An additional feature of the invention is the simplicity of the installation required at the difficult-to-access location. An additional significant advantage lies in the elimination of cross-talk, so often a serious problem in remote measurement systems. The invention presents a unique arrangement featuring a simple yet effective transducer configuration having few parts and thus high reliability.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to transducer sensor measurement and 
display systems, and more particularly to such systems for measurements 
made at difficult to access locations. 
2. Description of the Prior Art 
Transducer measurement and monitoring systems are known in which a sensor 
is located in extreme environment, difficult to reach places. One common 
application of such systems provides for transmission of well logging data 
from the borehole of a well. Still others provide for the pick-up of 
seismological data from multiple subterranean locations. These prior art 
devices vary in complexity from systems utilizing a multiconductor cable, 
where one conductor of the cable is utilized to transmit one measured 
parameter and having a complete transmitter located in the borehole, to 
systems using a monoline cable on a time-shared basis. 
While presently available systems can perform the function of remote 
measurements, some disadvantages of these prior art systems include their 
complexity, unreliability and tendency to malfunction. Most are pulse 
coded systems requiring synchronization signals and a relatively large 
number of active components at the measurement location. Among other 
things, these systems suffer from the ambiguities caused by cross-talk, 
noise and pulse overshoot problems. Most of these prior art devices have 
met special needs as presented by specific problems and have thus served 
narrow purposes. Some of these prior art devices have been described in 
the following listed patents that were brought to the attention of the 
Applicant through a novelty search conducted in the United States Patent 
and Trademark Office: 
1. U.S. Pat. No. 3,725,857 -- "Means and Method for Time-Sharing 
Multichannel Well Logging" -- Robert W. Pitts, Jr. 
2. U.S. Pat. No. 3,727,179 -- "Data Transmission Responsive to 
Synchronization Signal" -- Kenneth A. Bennett 
3. U.S. Pat. No. 3,652,979 -- "Installation for the Transmission of 
Multiplexed Seismic Signals" -- Philippe Angelle 
4. U.S. Pat. No. 3,309,657 -- "Dual Channel Well Logging System" -- William 
R. Rabson et al. 
5. U.S. Pat. No. 3,122,707 -- "Discriminator for Frequency Modulated 
Seismic Signals" -- Josiah J. Godbey 
It would thus be a great advantage to the art to provide a new and improved 
information system useful in locations which are difficult to access. 
Another great advantage to the art would be the provision of such a system 
in which there is no cross-talk between measurement channels. 
A further desirable advantage to the art would be the provision of such a 
system requiring only a simple installation at a difficult-to-acess, 
extreme environment location. 
An additional important advantage to the art would be the provision of such 
a system in a relatively uncomplicated and inexpensive yet reliable 
package. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a new and improved dual 
channel information system useful in locations which are difficult to 
access and which exhibit extreme environmental conditions. 
A further object of this invention is to provide a new and improved dual 
channel information system wherein information from both channels may be 
transmitted without requiring any additional conductors in a cable over 
the requirements for one-parameter transmission. 
Another object of the present invention is to provide a new and improved 
dual channel information system with no cross-talk between channels. 
A still further object of this invention is to provide a new and improved 
dual channel information system requiring only a simple installation at 
the difficult-to-access location. 
An additional object of the present invention is to provide the aforestated 
objects in a relatively uncomplicated and inexpensive yet reliable system. 
In the accomplishment of these and other objects, a transducer monitoring 
system is provided in which at least two measurements are completed in 
locations which are difficult to access. This system has the capability of 
making these measurements in remote locations under extreme environmental 
conditions. An important feature of the invention is the simplicity of the 
installation required at the difficult-to-access location. The simple yet 
effective transducer configuration has high reliability as a result of 
using very few active parts at the remote, extreme environment location. 
Typically the transducer assembly consists of two transducers, commonly a 
temperature transducer and a pressure transducer, and two diodes. The 
physical location of the transducer assembly may be in an oil well, for 
example, several thousand feet below the earth's surface. A communication 
line connects the transducers with a surface unit. This communication line 
may be a one-wire line using the earth as a return, or it may be a 
standard two-wire line, or alternatively it may consist of a three-phase 
power line which is spliced into at both the surface location and the 
downhole location. The surface unit typically consists of an electronic 
switch, current sources, a sample and hold module, a computing module, a 
display means, and a timing module. In one position of the electronic 
switch a current is caused to flow in one direction through the transducer 
assembly. In another position of the electronic switch a current is caused 
to flow in another direction through the transducer assembly. The results 
of these two current flows are monitored by the sample and hold module 
whose output is operated upon by a computing facility and then displayed. 
The transducer assembly, which due to the simple configuration, is highly 
reliable, is superior to any existing device.

DETAILED DESCRIPTION 
Although specific embodiments of the invention will now be described with 
reference to the drawing, it should be understood that such embodiment is 
by way of example only and merely illustrative of but a small number of 
the many possible specific embodiments which can represent applications of 
the principles of the invention. Various changes and modifications obvious 
to one skilled in the art to which the invention pertains are deemed to be 
within the spirt, scope, and contemplation of the invention. 
Transducers having elements whose output ratios are dependent upon the 
value of applied physical phenomena are well-known in the art. For 
example, a diaphragm in a pressure transducer, subjected to an incident 
pressure, will cause movement of a potentiometer wiper along its 
resistance element such that the position of the wiper along that element 
gives an indication of the magnitude of the incident pressure. A 
bimetallic element in a temperature transducer, subjected to an incident 
temperature, will likewise cause movement of potentiometer wiper so as to 
give an indication of the magnitude of the incident temperature. Such 
transducers have been used to measure such diverse physical phenomena as 
light frequency (colorimeters), position (gyroscope pickoffs), 
acceleration, pressure and temperature to name but a few. The use of 
general and conventionally well-known transducers are contemplated in the 
present invention. 
Assume that electronic switch 6 is in position 6a where current source 8 is 
activated through lead 34. It will be assumed that the line resistance 
R.sub.L is known. Current will then flow from current source 8 through 
line 34 to electronic switch contact 6a through a line 30 through 
communication cable 5b and into junction 38 of transducer assembly 14. 
This current will continue through diode 4 through transducer resistive 
element 1 whose resistance varies as a function of a physical phenomena, 
here exemplified as temperature through junction 32 through transducer 
resistive element 2 whose resistance varies as a function of a physical 
phenomena, here exemplified as pressure and out through junction 40 and 
through the other side of communication cable 5a through a line 36 and 
back into current source 8. Current sources 7 and 8 are capable of 
providing a known or measurable current value. The voltage V.sub.1 now 
seen by sample and hold circuit 9 by means of a line 18 is given by the 
relation: 
EQU V.sub.1 = I (R.sub.L + R.sub.t + R.sub.p) + V.sub.d4 
where V.sub.d is the voltage drop across the diode 4. This voltage V.sub.1 
will now be sampled and held in sample and hold module 9. If now 
electronic switch 6 shifts to position 6b, current source 7 will be 
engaged. Current will now flow through communication cable lead 5a and 
into junction 40 of the transducer assembly. This current will continue 
through transducer resistive element 2, whose resistance varies as a 
function of the same physical phenomena as noted above and through diode 
3, and out of junction 38 through communications cable line 5b, through 
lead 30 back through switch contact 6c into switch contact 6b and through 
lead 28 back into current source 7. It will be noted that this current 
does not flow through transducer resistive element 1 because of the back 
bias of diode 4. The voltage as sensed by sample and hold module 9 at lead 
18 is now V.sub.2 where V.sub.2 is equal to: 
EQU -I (R.sub.L + R.sub.p) - V.sub.d3 
This voltage is also sampled and held in module 9. Computing module 10 
receives data from sample and hold module 9 by means of a lead 22. 
Computing module 10 now adds V.sub.1 and V.sub.2 obtaining: 
EQU V.sub.1 + V.sub.2 = I R.sub.L + I R.sub.t + I R.sub.p + V.sub.d - I R.sub.L 
- I R.sub.p - V.sub.d 
Since V.sub.d3 is equal to V.sub.d4, the numerical subscripts can, and 
therefore have been, dropped. Thus, 
EQU V.sub.1 + V.sub.2 = I R.sub.t 
The resistance of transducer R.sub.t being known since R.sub.t = (V.sub.1 + 
V.sub.2)/I, it is possible to transform the resistance value directly to a 
temperature value because resistance is a direct function of temperature 
in the transducer which is measuring the physical phenomena. The 
temperature T is now known and may be supplied to display unit 11 by means 
of lead 24 from computing circuit 10. Since in addition to the 
temperature, the current I is also known, the voltage across the diode 
V.sub.d is also known. The computing module 10 can now substitute the 
values for V.sub.d and R.sub.L in the equation for V.sub.2 to solve for 
R.sub.p. Both pressure and temperature, since they are now known, may be 
processed in computing circuit 10 and presented to display module 11 by 
means of a cable lead 24. Timing module 12 communicates with display 
module 11, computing circuit 10, sample and hold module 9, and the 
electronic switch 6 by means of cables 20 and 26 interconnected as shown 
in the figure. The timing module 12 thus controls switching, sampling, and 
display, and so forth. The surface unit denoted generally by numeral 16 
usually will contain all the components such as electronic switch 6, 
current sources 7 and 8, sample and hold module 9, computing circuit 10, 
display means 11, and timing and control module 12. 
In locations such as oil wells, it is very expensive to add additional 
wires for transducer monitoring, and also due to severe environment 
temperatures of approximately 200.degree. C., it is extremely important 
that the transducer assembly complexity be kept to a minimum. Mechanical 
switching devices such as relays should not be used in the downhole 
locations and neither should devices such as transistors or operational 
amplifiers for maximum reliability. A feature of the present invention is 
its removal of all complexity from the transducer assembly to the surface 
unit where environmental conditions and accessibility are less extreme. 
Thus, there has been described a transducer monitoring system that will 
find use in locations which are difficult to access and which exhibit 
extreme environmental conditions. Great improvements in reliability, 
flexibility, maintainability, ease of operation and so forth have been 
provided through the novel advantages of the invention. 
It is pointed out that although the present invention has been shown and 
described with reference to particular embodiment, nevertheless various 
changes and modifications obvious to one skilled in the art to which the 
invention pertains are deemed to lie within the purview of the invention.