F0RM2
THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)
1. Title of the invention: : A TEMPERATURE SENSING ARRANGEMENT FOR
USE IN TEMPERATURE COMPENSATION IN FUEL DISPENSERS


2. Applicant(s)
(a) NAME :
(b) NATIONALITY:
(c) ADDRESS:

Larsen & Toubro Limited
An Indian Company.
L & T House, Ballard Estate, Mumbai 400 001 State of Maharashtra, India

3. PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed:


TITLE OF THE INVENTION
A TEMPERATURE SENSING ARRANGEMENT FOR USE IN TEMPERATURE COMPENSATION IN FUEL DISPENSERS
TECHNICAL FIELD OF THE INVENITON
The present invention relates to a temperature sensing arrangement for temperature compensation in fuel dispensers. More particularly, the invention is concerned about a sensing arrangement for measuring the amount of fuel dispensed accurately compensating for any change in volume arising due to variation in ambient temperature. In the present embodiment the invention is described with respect to ftiel being dispensed from a fuel dispenser. However, this system is capable of being used in any other dispensing operation for any other fluids. The invention is further concerned about an arrangement for sensing temperature which would be able to provide explosion proofing to the digital temperature sensor used for temperature compensation in fuel dispensers.
BACKGROUND OF THE INVENTION
Temperature compensation is done in fuel dispensers so as to compensate volume difference which arises because of temperature variations. For accurate temperature compensation, accurate measurement of fuel temperature is necessary.
To measure temperature of fuel explosion-proof temperature probe is used. Analog temperature sensor like PT-100, thermocouple is embedded inside this temperature probe.

Disadvantages of analog sensor :
1. Need of complex signal conditions circuit.
2. Prone to noise & transmission errors.
3. Gets affected by electromagnetic interference.
4. Restriction on cable length.
5. Need of factory level calibration and system level calibration for each individual sensor, which needs skilled labor.
6. Error which arises because of component tolerances
Advantages of digital sensor:
1. No need of complex signal conditioning circuitry.
2. Digital output is free from errors because of noise and electromagnetic interference.
3. No restriction on cable length.
4. The accuracy of the digital sensor is guaranteed by the manufacturer and hence no separate calibration needed.
It has been found that the digital sensor for fuel temperature measurement has several disadvantages. The disadvantages are discussed hereinbelow :

1. Cannot be immersed in the fuel. This is because even a very small current flowing through current (in mA) may cause spark which can ignite fuel, and lead to explosion. So as per safety standard, sensor carrying power supply line cannot be directly immersed in the fuel.
2. Most of the digital temperature sensors needs supply voltage for its operation, which again makes it not suitable for intrinsically hazardous environment. (In analog sensors, say PT100, resistance of PT 100 changes as temperature changes, making it suitable for fuel temperature measurement.)
3. Generally digital sensors are designed for ambient temperature measurement.
4. There are digital sensors available for fuel temperature measurement, but they are NOT designed to give instantaneous temperature reading. Such sensors are known as MButtons'. These sensors are put inside fuel for required time. Then they are taken out to read temperature value. It then shows log of temperature readings at different time. So instantaneous temperature cannot be read and used for further processing. So such sensors cannot be used in applications, which depend on instantaneous temperature reading for further processing e.g. temperature compensation.
It was found that when sensors are directly put inside the thermowell then :
1. Results are not accurate (i.e. accuracy is not within +/- 0.5 deg C) Thus making it unsuitable for temperature compensation, (for temperature compensation accuracy of+/- 0.5 deg c is necessary)

2. Low sensitivity (Sensitivity is change in temperature reading shown by the sensor with respect to change in temperature of fuel.)
3. Settling time is more.(Settling time is time required by the sensor to settle down at stable reading).
4. Settling time is non-linear, i.e. settling time is more at higher and lower temperatures as compared to room temperature. Also there is no fixed pattern between temperature and settling time. This makes sensor unreliable for variety of temperature ranges.
5. Poor thermal insulation from environment, i.e. external environment temperature cause error in temperature measurement of fuel.
Like any other liquid, fuel undergoes expansion and contraction with temperature change. Because of this actual fuel dispensed varies with temperature. Considering the ever increasing cost associated with fuels, it is quite important to measure the amount of fuel being dispensed accurately compensating therefore, any change in volume arising due to ambient temperature variations.
Conventionally temperature compensation systems were developed and deployed independent of fuel dispenser electronics. The compensation involves two steps-
a. temperature measurement
b. Compensating the volume measured with respect to standard room
temperature and display to the customer

In most temperature compensation systems, analog temperature sensors like PT100 or thermocouple is used. The property of linear change in resistance of the sensor element with respect to temperature is used to measure the temperature.
All the previous temperature compensation techniques use analog temperature sensor as discussed hereinabove. However, digital sensors were also known to exist but the same suffer from the disadvantages as described above.
Typical block diagram for all the previous systems:
Analog sensor output -> Signal conditioning circuit -> Microcontroller
<-Calibration<- ^- Calibration <-
In analog sensors e.g. PT-100, resistance changes with change in temperature. A constant current source is connected to this resistive element. So voltage across PT-100 resistance changes with temperature. This voltage is further amplified and conditioned and finally given to microcontroller for further processing.
Calibration Requirements for Analog sensing system:
The Pt-100 sensors require factory calibration certificates and there could be variation in the measured value from sensor to sensor. Also due to the tolerances of the components used in signal conditioning circuitry a factory level calibration is required to further fine-tune the output measured. Thus Analogue system required two stage calibration processes which demands a skilled labour.
In view of the above shortcomings/disadvantages of the analog and also in the arrangement of digital sensors there exist a need to provide for a sensing arrangement for measuring the amount of fuel dispensed accurately compensating for any change

in volume arising due to variation in ambient temperature. Further there is a need for an arrangement for sensing temperature which would be able to provide explosion proofing to the digital temperature sensor used for temperature compensation in fuel dispensers.
OBJECTS OF THE INVENTION
Accordingly, one object of the present invention is to overcome the disadvantages / drawbacks of the prior art.
Another object of the present invention is to provide a sensing arrangement for measuring the amount of fuel dispensed accurately compensating for any change in volume arising due to variation in ambient temperature..
Another object of the present invention is to use minimum operating voltage and current.
Yet another object is to provide asset management feature in the arrangement.
SUMMARY OF THE INVENTION
According to one aspect of the present invention there is provided a sensing
arrangement for measuring the amount of fuel dispensed accurately compensating for
any change in volume arising due to variation in ambient temperature, said
arrangement comprises :
microcontroller;
temperature sensor means being operatively connected to said micro-controller; and
thermowell

wherein said temperature sensor means being located inside said thermowett in a manner that explosion proofing is provided to said sensor means wherein said thermowell comprises insulating means being provided intermediately between said temperature sensor means and thermowell.
The other objects and advantages of the present invention will be apparent from the description provided hereinbelow with reference to the accompanying figures and detailed description provided hereinbelow.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 illustrates a block representation of the arrangement of the present invention.
Figure 2 illustrates cross sectional view of the sensing assembly of the system of the present invention.
Figure 3 illustrates a typical performance curve showing accuracy of dispensing of fuel.
Figure 4a and 4b illustrates various topologies showing connection of one or more temperature sensors.
Figure 5 illustrates sequence of operation in the system of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The arrangement for measuring accurate dispensing of fuel from the dispenser comprises micro-controller and temperature sensor. The temperature sensor is kept inside specially designed enclosure.

1. Microcontroller: Any microcontroller (7) that has a bidirectional 10 line can be used.
2. Temperature sensor: Sensor (1) used is Maxim's I-Wire digital temperature sensor. It has following features:
■ • Temperature range: -55°C to +125°C
• Converts temperature to digital word in 200 ms
• Requires no external components
• Works on 1 -Wire protocol
• No power supply pin, works on parasite power supply
• Perfectly suitable for explosive environment since power supply line does not go to sensor element.
• uC to sensor interface requires just two wires (Data and GND)
Typical Performance Curve
A typical performance curve is figure 3. In fuel dispensing applications, typical temperature measurement range is -5 to 65°C. From above curve it is clear that the accuracy can be as high as ±0.1 °C can be achieved within this range.
Sensor used here works on industry standard I-wire protocol. Detailed description of this 1-W algorithm is given. But one cannot put this sensor directly in contact with liquids. So it is kept inside a specially designed thermowell. Since the output of this sensor is digital, there is no restriction on cable length since output is not affected by electromagnetic interference or stray capacitance of cable.

3. Explosion-proof thermowell: The sensor (1) is put inside a specially designed explosion proof thermowell (2) so that it can be kept in contact of explosive liquids. As shown in fig2, temperature sensor (1) is kept inside specially designed thermowell made up of SS. An insulating paste (3) is filled between sensor element (1) and thermowell (2). This assembly is well sealed so that it is IP67. The thermowell (2) further comprises solder contacts (4) and thermal insulator (5). A cable (6) containing encrypted temperature is taken out from this assembly. Further processing id done by micro-controller. V number of temperature sensors connected on the same bus using various topologies are shown in figures 4a and 4b. Short stub topology and star topology are shown in figures 4a and 4b respectively.
The properties of special insulating paste of the thermowell are :
• Bad conductor of electricity and heat.
• Thermal conductivity in the range of 30 to 150 W/mK. Thermal conductivity should be more than 30 W/mK so that it leads to proper and accurate results.
• Some of the compounds and their respective thermal conductivities are mentioned below:

1. Aluminium oxide - 39 W/mK
2. Aluminium Nitride - 170 W/mK
3. Beryllium Oxide-218 W/mK
However, the above compounds do not restrict the scope of the present invention and other similar compounds having thermal conductivity in the range as mentioned can be used and still the invention can be performed.

General Working:
1. First handshaking is done between microcontroller and 1-Wire temperature sensor as per 1-Wire protocol. 1-wire protocol is explained in detail later on this article.
2. After successful handshaking, present temperature is sent by temperature sensor.
3. This temperature is in 12 bit digital signal.
4. Microcontroller then processes this digital temperature reading. Then routine temperature compensation is followed.
1-Wire Protocol:
The master device or microcontroller initiates and controls all activities on the network bus. This is why it is known as the bus master. The bus master acts as a protocol and timing interface between a PC or microcomputer and the 1-Wire network. Both the bus master and all slave devices internally act as transceivers. These are devices that can both send and receive data on a single data line. One can think of this single communications line as a single lane road, where traffic takes turns, first going one way, then the other. So data can flow in either direction, but only one direction at a time (half duplex operation). Data transfers are bit sequential with the least significant bit of a byte being transmitted first, over a single pair of wires, a data and a ground return line. Synchronizing of the devices is handled by the 1-Wire data protocol (regulating who talks and who listens at any given time). This allows tight control of the data bus because the protocol allows no slave to speak unless requested by the master, and then communication is only allowed between the selected slave and the bus master; no communication is allowed slave to slave.

1-Wire communications takes place digitally (on or off logic states), over a wire cable (typically twisted pair). The network is defined with an open drain (wired-AND) master/slave multi-drop architecture that uses a resistor pull-up to a nominal 3.3 Volt supply at the master.
The system uses 1-Wire protocol as published by Dallas Semiconductor. The brief explanation as given by Dallas Semiconductor is as follows.
1-Wire signals require a strict protocol to insure data integrity. The bus master as mentioned before initiates all communications on the bus. The basic 1-Wire protocol consists of four types of signaling on the data or OWIO line: These are
1. Reset Sequence with Reset Pulse and Presence Pulse
The reset pulse is used to put all devices on the 1 -wire bus into a known state. When a slave, or slaves, sees the Reset Pulse, they acknowledge receipt by returning a Presence Pulse to indicate their "presence" or existence in an active state on the bus.
2. Write 0
Send a '0' bit to the 1-Wire slaves (Write 0 time slot).
3. Write 1
Send a * T bit to the 1-Wire slaves (Write 1 time slot)
4. Read Data
Read data sequences are similar to the write 1 time slot but the bus master samples the bus state after it releases the line to read data back from a slave device. In this manner it is able to read back either a 0 or a 1 from the slave.

Advantages of Digital Sensing System:
• The accuracy of the digital sensor is guaranteed by the manufacturer and hence no separate calibration needed
• The typical currents involved in the measurement are in micro amperes, reducing any remote chances of explosion; hence making the measurement process safer.
• The length of sensor from the measurement system can be as long as 20 meters as specified in the protocol. Hence a single controller unit can handle multiple temperature compensation inputs on a typical site.
• The digital sensor works on minimal operating currents (up to 1.5 mA max ) and voltages (3.3V typical) compared to analogue sensors thus reducing the possibility of explosion
• Need for 'Self-Designed' system: For higher security self designed system is any time advantageous.
• Need for asset management: Latest systems provide this feature so as to make system modular and flexible. So there is need for such a system which can provide asset management feature to temperature sensor.

WE CLAIM
1. A sensing arrangement for measuring the amount of fuel dispensed accurately
compensating for any change in volume arising due to variation in ambient
temperature, said arrangement comprises :
microcontroller;
temperature sensor means being operatively connected to said micro¬controller; and thermowell
wherein said temperature sensor means being located inside said thermowell in a manner that explosion proofing is provided to said sensor means wherein said thermowell comprises insulating means being provided intermediately between said temperature sensor means and thermowell.
2. Arrangement as claimed in claim 1, wherein said insulating means of the thermowell comprises insulating paste.
3. Arrangement as claimed in claims 1 and 2 wherein said insulating means selectively comprises aluminium oxide, aluminium nitride, beryllium oxide and the like.
4. Arrangement as claimed in claims 1 to 3 wherein said thermowell has thermal conductivity of atleast 30 W/mK.
5. Arrangement as claimed in claims 1 to 4 wherein said thermowell has thermal conductivity ranging from 30 W/mK to 150 W/mK.
6. Arrangement as claimed in any of the preceding claims wherein said sensor is a digital sensor.

7. Arrangement as claimed in claim 6 wherein said digital sensor is Maxim's 1-wire digital temperature sensor.
8. Arrangement as claimed in claim 1 wherein said micro-controller comprises bi-directional input/output line,
9. A sensing arrangement for measuring amount of fuel dispensed accurately compensating for any change in volume arising due to variation in ambient temperature as herein substantially described and illustrated with reference to the accompanying figures.


Dated this the 31st day of December 2008