FIELD OF THE INVENTION
The present invention relates to a system for modification of unbalanced signals from sensor assembly to provide improved signal to noise ratios.
BACKGROUND OF THE INVENION
Automated process control has become widely implemented in virtually all large-scale industrial manufacturing units. Automated decision making to control optimum process parameters eliminated several man machine interfaces and reduced the chances of operator error. With ever powerful computational resources available, complex process parameters are decided upon by coded algorithms. However the accuracy level of these control algorithms is highly dependent on the error in measured process parameters being input to this system. Erroneous data being fed into any process control system would result in atleast sub-optimal performance or atmost result in damage to property and lives.
However, use of online and in-situ electronic sensors has been commonplace in industries for over half a century. Human operators were responsible for variously interpreting the reading of each sensor and decision was taken accordingly. In the last decade, the innovation that has occurred is replacement of a human operator with a digital decision making. This has happened at a fast pace as computers can easily be fed electronic signals directly, and can also provide control signals with equal ease. Since new and improved algorithms can be loaded very quickly, and improved upon, acceptance of digital process control has occurred rapidly. While control systems relying on coded algorithms are precise and reliable, the sensors and associated hardware often does not measure up, and provides erroneous data which the algorithm cannot interpret as such. A human operator on the contrary is better able to judge an arriving data as an exception or faulty by virtue of his / her experience. This ever-increasing requirement for accurate and reliable sensor data from an industrial process has led to the development of a huge array of new sensor and associated technology.
While installation of computers and frequent upgradation of control software has become common, replacement of pre-existing sensors, cables and other hardware

components or their technology as a whole has occurred at a much slower pace. The cost involved in replacement of sensors, the logistical and safety issues involved, often in hazardous industrial conditions, and simply there being no possibility of replacement, among other reasons have contributed to this. Thus it is common to find control systems relying on sensors which predate the latter often by decades.
A common and lingering problem associated with prior art sensors is the presence of electrical noise superimposed on the signal. This results in poor signal to noise ratio. Additionally, the baseline level of this noise varies widely in amplitude depending on ambient electromagnetic interference in the environment, hereon referred to as noise. While shielding all signal cables and using twisted pairs eliminates some of the noise, they are at times insufficient in high noise environments, commonly encountered in heavy industries. Use of balanced cables, an example of which is cited in patent US 5831210A and US 5109415A, provides a good method of noise suppression. In case of balanced signals common mode rejection ensures only the actual signal is allowed to pass through into the control system. Since noise signals originating as a result of external electromagnetic interference affects both wires of a balanced cable equally, it can be rejected by several digital and analogue means, several examples of which are described in the documents US 6566946B2 and WO 2000041297A1. As mentioned previously, there still exist a large number of analogue sensors which are not configurable to provide output via a balanced cable, either by virtue of its technology and design, or other hardware limitations. This is especially true with sensors of high impedance, including but not limited to microphones.
OBJECT OF THE INVENTION
It is an object of the invention to propose a system for modification of unbalanced signals from twin terminal analogue sensors to provide improved signal to noise ratios.
SUMMARY OF THE INVENTION
Depending on the type of sensor, the quality and type of wire, and the levels of noise in the environment, the final signal received at the control system consists of the true signal along with a variable amount of noise. Under normal circumstances it becomes

impossible to differentiate actual signal from background noise, without having a measure of the noise being determined. The present invention proposes lying of one or more additional balancing conductive loop also refered to as the balancing cable, whose electrical characteristics matches that of the primary conductive loop also referred to as the primary cable, but comprising of purely resistive elements. The signal cable and balancing cable being in close proximity to one another. This is to ensure that identical levels of noise are picked by both cables. The balancing cable being terminated in a resistive element does not pick up any signal by virtue of changes in its environment, unlike the primary cables, which is effected by both changing environmental parameters which the sensor is designed to register, as well as noise. Thus the balancing cable in question faithfully provides information about the noise signature contained in the actual signal. To implement the common mode noise cancellation, the two signals can be variously subtracted from one another to cancel the noise contained in the original signal. Depending on the type, number and location of sensors utilized, a wide variety of cable types and layouts may be installed. The present invention proposes that one or more balancing cable can provide a sufficiently accurate measure of noise to be used in the said technique.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 – shows an embodiment of the invention where a single sensor connected by an unshielded twisted pair.
Figure 2 – shows another embodiment of the invention where a single sensor is originally connected by a coaxial cable, after modification, is replaced by a shielded twisted pair.
Figure 3 – shows a further embodiment of the invention where a plurality of sensors are connected by an array of twisted pair comprising a single cable.

DETAILED DESCRIPTION OF THE INVENTION
A generic sensor assembly and control system comprises a sensor (1)(Figure 1) located at or close to the process intended to be controlled, a primarycable, of type twisted pair (2) which conveys the signal to an analogue to digital converter (3) and a digital processer/ computer (4). The sensor in has an internal resistance of Rint ohms and is of an analogue type which generates a measurable signal in response to the type of stimulus; for example, the sound pressure in case of a microphone. Let V1 be the instantaneous voltage being recorded at the data logger. The length of the cable (2) travels through an environment with heavy electrical noise, and this induces interference in the signal resulting in poor signal to noise ratio. The signal thus consists of a true signal superimposed on an induced noise. The present invention proposes laying of a second pair of twisted pair, a balancing cable (5), in close proximity of the former along its length in entirety. The open end of the cables terminating in the vicinity of the sensor being connected with a resistance (6) equal to Rint; and the other end being connected to a separate channel on the data logger. Let the instantaneous voltage being recorded by this balancing cable be Vbal. Both V1 and Vbal being logged, a common mode noise cancellation can be accommodated within the control algorithm to the following relation

Where Vsignal would hereafter be treated as the original from the sensor the noise component having being eliminated.
In another embodiment of the invention which utilizes, a shielded coaxial wire (6)(Figure 2), works to eliminate a large amount of electrical noise, nevertheless, the signal is often not of sufficiently high quality in spite of the shielding. For further improvement of signal to noise ratio, a shielded twisted pair (7) may be substituted for the signal cable while retaining the remaining hardware components. In this setup The shield and one of the internal conductors is connected to the terminals of the sensor, and the shield and remaining internal conductor acting as the balancing cable, being terminated in a

resistance Rint, placed in close proximity to the senor. Both signals being captured on separate channels of the data logger and then subtracted from one another to incorporate common mode noise rejection.
In another embodiment of the invention (Figure 3) a plurality of sensors are installed in a region, and each signal being carried by an array of twisted pair collectively forming single enclosed cable(8).In this case, the said cable should be made to contain an additional unused twisted pair which would be utilized as a balancing cable. One end of which should terminate at a resistance (9) placed in the vicinity of the sensors and having a value RbalOhms which would be an arithmetic mean, or some other measure of central tendencies of the internal resistances of the sensors. Let V1, V2, V3 ….. Vn, be the instantaneous signal voltages being measured at the data logger and Vbalbe that for the balancing cable. Then common mode noise rejection for each sensor signal can be implemented by using the relation
Where
Vsignal,n is the signal from the nth sensor after noise cancellation
Rint,n is the internal resistance of the nth sensor.
Value of α being closer to unity, the better the performance of the invention.
In another embodiment of the invention a plurality of twisted pairs are used to convey signals from an array of sensors, to the analogue to digital converter, with each twisted pair being enclosed severally with a conductive shield to eliminate noise. In this arrangement, the balancing cable would additionally have similar shielding characteristics as the primary cables.
In another embodiment of the invention, metallic shielding surrounds each twisted pair severally, or the signal cable and all its conductors in its entirety or any permutations and combination thereof. In this arrangement, the nature and layout of the balancing

cable would remain identical to the remainder of the primary cables and additionally share similar shielding characteristics.
Another embodiment of the invention, utilizes a plurality of unpaired conductors where separate conductive elements convey signals from one sensor terminal to the analogue to digital converter, the remaining terminal being connected to the said analogue to digital converter by a singular conductive element, hereafter referred to as common ground, which is shared by all sensor elements. In this arrangement a single unused conductor and the common ground can act as a balancing cable. The methodology and common mode rejection algorithm being identical to one described in preceding sections.
In another variation of a sensor based control system, a large number of diverse sensors are located at several locations each connected by separate sensor cables of different types. In this arrangement a separate twisted pair terminating in a resistance Rbalmay be laid such that it faithfully represents the signature of the noise, and noise cancellation being implemented by the same relation described previously

Here the value αtrial being selected by experimentation such it the final signal yields the minimum amount of noise.
Although particular embodiments of the invention have been shown and described in full here, there is no intention to thereby limit the invention to the details of such embodiments. On the contrary, the intention is to cover all modifications, alternatives, embodiments, usages and equivalents as fall within the spirit and scope of the present invention, specification and appended claims.

WE CLAIM
1. A system for improvement of signal to noise ratio of unbalanced signals
comprising
A one or more balancing conductive loop, the balancing conductive loop being composed of pure resistive element positioned in close proximity to a the primary conductive loop, the balancing conductive loop having electrical and physical characteristics similar to primary conductive loop which conveys the unbalanced signal,
the said one or more balancing cable yielding common mode noise signals, or a plurality of mathematically related measures thereof, and having sufficient characteristics to realize common mode noise cancellation by digital signal processing techniques post to data acquisition.
2. The system as claimed in claim 1, wherein, the one or more balancing
conductive loop comprising
a fixed resistor interposed along the one or more balancing conductive loop to match the resistance of the primary conductive loop; and
common mode noise cancellation being realized by direct scalar subtraction of the two signals; post to data acquisition.
3. The system as claimed in claim 2, wherein the primary conductive loop and the one or more balancing conductive loop identically are electromagnetic shielded identically
4. The system as claimed in claim 1, wherein one or more balancing conductive loop have common ground same as that of the primary conductive loop, if used.
5. The system as claimed in claim 1, wherein

a fixed resistive element being interposed along the one or more balancing conductive loop, the resistance being equal to a suitable measure of central tendency of the resistance of the primary conductive loop;
common mode noise cancellation being implemented by the relation Vn - αVbal where Vn and Vbal are the signal levels of the nth primary conductive loopand one or more balancing conductive looprespectively, the value of α being variously obtained so as to minimize background noise in each signal.
The systemas claimed in claim 5, wherein the measure of central tendency is the mean of the resistance of the primary conductive loop
common mode noise cancellation being implemented by the relation Vn -(Rn/Rbal)Vbal where Vn and Rn are the signal level and resistance of the nth primary conductive looprespectively and Vbal and Rbal the signal level and resistance of the one or more balancing conductive loop respectively.