|Title of Invention||
AN IMPROVED DEVICE USEFUL FOR MAKING METHANE SENSOR
|Abstract||An improved device useful for making a methane sensor which comprises in combination of a platinum wire coil (1) has the diameter on the range of 1 to 2 mm, the said coil being encapsulated in a known alumina, the said platinum wire has a diameter in the range of 46 to 50 SWG, the said platinum wire encapsulation coil of alumina (5) surface having a coating of known catalyst of platinum, palladium an d earth metal in the range of 1:1 to 1:5 and rare.|
|Full Text||This invention relates to an improved device useful for making a methane sensor.
The invention particularly relates to an improved pellistor and a low power catalytic type methane sensor using the pellistor. This sensor is useful for mines or areas having explosive atmosphere such as petrochemical industries.
It is hither to known to manufacture low power methane sensor having power consumption in the range of 0.5 to 1 W and having a response of 30-45 mV when connected in a wheat stone bridge operating with power supply having a minimum voltage of 2.5 V and exposed to 5% methane.
This above sensor has the drawback such as : i. The sensor uses 2.5 to 3V and 0.5 to 1 W of power.
ii. The output of the sensor is generally low, to the extent of 30-45 mV at 5% methane. Larger values may be preferred.
iii. Use of flame proof (FLP enclosure in underground areas may not be preferred if intrinsically safe circuit can be designed. When measuring methane continuously power supplies on a continuous basis creates a problem.
iv. Placement of local batteries underground creates problems while having continuous measurement of methane.
v. While using chargeable batteries for continuous measurement of methane, charging from surface requires additional pair of cable thereby increasing the cost of the system.
vi. These arrangements as described at (iii) to (v) require more electronic equipment underground which is not desirable from maintenance point of view.
The object of the present invention is to provide an improved device (pellistor) useful for making a methane sensor incorporating the said device which obviates the above noted drawback.
Our research and development efforts have shown that:
1. It is possible to develop catalytic bead type methane sensor which works
on 1.5 to 2.0 volts consuming 200 to 300 mA and having power
consumption ranging from 0.3 to 0.6 watts.
2. It is possible to work out a circuit in such a way that the sensor may work
on continuous AC/DC or intermittent DC.
3. It is possible to get output of the sensor over 75 mV at full scale deflection
of 5% methane using continuous D.C.
4. The output is 60 mV at intermittent D.C. maximum having maximum ON-
OFF cycle of 100 milliseconds at full scale operation.
5. The circuit may employ a signal processor to give TTL level output, in
case TTL level output is needed for remove operation.
Accordingly the present invention provides an improved improved device useful for making a methane sensor which comprises in combination of a platinum wire coil (1) has the diameter on the range of 1 to 2 mm, the said coil being Encapsulated in "a known alumina, the said platinum wire has a diameter in the range of 46 to 50 SWG, the said platinum wire encapsulation coil of alumina (5) surface having a coating of known catalyst of platinum, palladium and rare earth metals in the range of 1:1 to 1:5.
The catalyst of platinum, palladium and rare earth metals are in ratio in the range of 1:1 TO 1:5, rare earth metals remaining in traces only and selected from thorium and cerium respectively. The cool may have a diameter in the range of 1 to 2 millimeter and the platinum wire may have a diameter of 46 to 50 SWG.
Accordingly, the present invention provides a methane sensor incorporating the improved pallistor.
A sensor can be safely used for continuous monitoring of methane using an intrinsically safe power fed intermitantly with the help of microprocessor switching. cor manual operation a 1.5 V to 2.4 V dry battery or Ni-Cd chargeable battery may be used.
The invention will now be described with the help of figure 1A, 1B and 2. In figure 2 Wheatstone bridge circuit is shown comprising of:
i. Two pellistors, one known as detector and other as compensator as shown in figure 1A as 1 & 2 forming the two arms of the bridge.
ii. The compensating resistance 3, 4 forming other two arms of the bridge, iii. One potentiometer 5 parallel with arm 3 and 4 for zero adjustment.
iv. One variable resistance 6 in sensor with a current meter calibrated in terms of methane percentage.
In the above description the pallistor is novel but the entire bridge circuit has been shown for the purpose of clarity. The pallistor is described below.
In figure 1A bare filament consisting of 2 to 10 turns of platinum wire of 46-50
SWG wound over a diameter of 1-2 mm has been shown. In figure 1B a pellistoris
formed first by depositing a layer of alumina and then coating with catalyst of
platinum palladium and rare earth metals. The ratio of the various ingredients ar in
the range of:
Platinum : Palldium as 1:1 to 1:5 the rare earth metals remaining in traces and selected from thorium and cerium.
The deposition of the catalysts is done very slowly to get alpha phase and is achieved with the help of control of current through the platinum coil.
Operation of the sensing unit:
Operation will now be described with the help of fig.2. The gas sample in mine or other explosive atmosphere diffuses through the sintered disc made of bronze having a diameters in the range of 1 cm to 5 cm and having a porosity in the range of 50-150 microns and passes into the diffusion chamber where it comes in contact with catalytic surface of the pellistor, Methane in sample undergoes a combustion reaction with the following general equation :
CH4 + 2O2 → CO2 + 2H2O
The heat so liberated changes the temperature of the pellistor thereby imbalancing the Wheatstone bridge, products of reaction from catalytic pellistor diffuse through the sintered disc in the reverse direction to create an equilibrium obtained within 15 to 20 seconds. The bridge is operated with a D.C. volts of 1.5 to 2 volt consuming 0.3 to 0.6 watts to create a combustion temperature as the range of 250°C - 350°C. The imbalance bridge voltage forms the basic measurement and calibrated in terms of methane concentration.
We claim :
1. An improved device useful for making a methane sensor which comprises in
combination of a platinum wire coil (1) has the diameter on the range of 1 to
2 mm, the said coil being encapsulated in a known alumina, the said platinum
wire has a diameter in the range of 46 to 50 SWG, the said platinum wire
encapsulation coil of alumina (5) surface having a coating of known catalyst
of platinum, palladium and rare earth metals in the range of 1:1 to 1:5 and
2. An improved device useful for making a methane sensor substantially as
herein described with reference to figs 1(a) & 1(b) the drawings
accompanying this specification.
|Indian Patent Application Number||176/DEL/1995|
|PG Journal Number||37/2003|
|Date of Filing||07-Feb-1995|
|Name of Patentee||SATISH CHANDRA SRIVASTAVA|
|Applicant Address||INSTRUMENTATION DIVISION, C.M.R.S. DHANBAD,INDIA|
|PCT International Classification Number||N/A|
|PCT International Application Number||N/A|
|PCT International Filing date|