HERE - Nemoto
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1. issue 4 Sept 2015 page 9 of 16 A High Temperature High Humidity The following graph illustrates the signal output stability for a sensor exposed to 50 C and 90 RH over 1100 hours The NH3 concentration used was 100ppm NHs in air 12096 gt 100 Eb E 8096 E 40 S 20 5 0 0 200 400 600 800 1000 1200 1400 Time h Low Temperature The following graph illustrates the signal output stability for a sensor exposed to 20 C over 10 000 hours The NHs concentration used was 10ppm NHis in air 140 120 OD 100 80 60 40 S 20 B 0 6 0 2000 4000 6000 8000 10000 Time h 3 Tolerance to thermal shock The following table shows the zero and sensitivity change following an exposure to 20 C for 30 minutes followed immediately with an exposure to 50 C for 30 minutes This 60 minute cycle was repeated 10 times The gas concentration used for testing was 100ppm After temperature cycling Sensitivity Sensitivity to Zero offset in air Sensitivity to variation ratio 100ppm NHs uA 100ppm NHs uA 96 NE4 NH3 Manual issue 4 Sept 2015 page 10 of 16 A 4 Tolerance to mechanical shock The following table shows the zero and sensitivity change following a drop test The sensor was dropped from a height of 1m on to a concrete floor 5 times The gas concentration used for testing was 100ppm Beforetest micro A test2. micro A After test micro A Sensitivity Zero offset in air Examen sue to Zero offset in Sensitivity to variation ratio 100 NHs uA air uA 100ppm uA 96 101 5 103 2 99 2 5 Tolerance to Sulphur Dioxide SO The following table shows the zero and sensitivity change following an exposure to 50ppm Sulphur Dioxide 502 for 120 minutes The gas concentration used for testing was 100ppm Before exposure After exposure Sensitivity Zero offset in air Sensitivity to Zero offset in air Sensitivity to variation ratio 100ppm NHs uA 100ppm NHs uA 6 Tolerance to Hydrogen Sulphide H2S The following table shows the zero and sensitivity change following an exposure to 50ppm Hydrogen Sulphide for 120 minutes The gas concentration used for testing was 100ppm Befoeexposue exposure After exposure Sensitivity Zero offset in air EN LS to Zero offset in air Sensitivity to variation ratio uA 100ppm NHs uA uA 100ppm NHs uA 9 6 NE4 NH3 Manual issue 4 Sept 2015 page 11 of 16 A 7 Tolerance to Nitrogen Dioxide NO The following table shows the zero and sensitivity change following an exposure to 50 ppm Nitrogen Dioxide NO2 for 120 minutes The gas concentration used for testing was 100ppm Before exposure After exposure Sensitivity Zero offset in air Sensitivity to Zero offset in air Sensitivity to Variation ratio uA 100ppm NHs uA uA 100 N
3. of force to the sensor Take care not to block the gas intake area as it may prevent gas entering the sensor Never put foreign material in the gas intake area as it may cause the electrolyte leakage Do not expose the sensor to excess vibration or shock If the sensor housing is damaged do not use the sensor After the sensor is exposed to high concentration gas for long periods the output signal may require time to recover to normal operation Do not blow organic solvents paints chemical agents oils or high concentration gases directly onto sensors Do not disassemble the sensor as this may cause electrolyte leakage DEFINITIONS Baseline Baseline shift Baseline means the output level in clean air The output current value at 209C would be less than 400nA but this tends to increase as the ambient temperature rises more than 309C The baseline shift means this variation of the output level i e a maximum of 1uA would be put out at 50 C This baseline shift should be taken into account to optimise overall accuracy In this manual the output values are calculated to be equivalent to NHs gas concentrations Gas sensitivity Output signals Using the NE4 NH3 40 12nA is generated at 1ppm of NHs gas For instance the generated current value will be about 1 2 at 100ppm of NH3 gas 100ppm x 40nA This generated current is generally recorded as a voltage produced by a Current Voltage converting circuit as illustrated in ou
4. in Storage NE4 NH3 Manual issue 4 Sept 2015 page 5 of 16 DIMENSIONS 20 4 2009 5 KON Pre ilter 16 6 9 0 1 5 4 3 s Reference electrode Di Working electrode Counter electrode 13 5 0 2 617 4 Case Material Cap Color Weight NE4 NH3 Manual issue 4 Sept 2015 page 6 of 16 A PERFORMANCE DATA 1 Uncompensated Temperature Dependence The following graph illustrates the typical effect of temperature on the output signal of the NE4 NH3 for a sensor calibrated at 20 C Nn Output of Signal at 20 C 2 ud c 40 40 30 20 10 0 10 20 30 40 50 Temperature C 3 Cross Sensitivities The following table gives cross sensitivity information for a variety of commonly encountered gases NH3 100 NE4 NH3 Manual issue 4 Sept 2015 page 7 of 16 4 Response Characteristics The following are plots of typical responses and recovery times for exposures to Ammonia at various gas concentrations 6 Output 1LA Time sec 5 Long Term Drift Characteristics The following graph illustrates the typical Long term sensitivity stability of the NE4 NH3 sensor over 420 days of operation 6 tun Output current jtA NH3 100ppm Ja Time h This data was gene
5. many applications involve the monitoring for leaks in pressurised ammonia lines or cylinders in refrigeration plants In such situations the gas can be initially very cool resulting in the leaking gas falling to ground level before rising when its temperature equilibrates with the surrounding atmosphere If the sensor is to be used in more irregular atmospheres please contact us for assistance 3 Storage of sensors Electrochemical sensors should be stored in a clean air under room temperature preferably 0 C 20 C and in non condensing RH conditions The maximum storage period would be 6 months after delivery For sensors stored for more than 6 months the life in service may be shortened by the excess storage period Unlike semiconductor type or hot wire type gas sensors the gas sensitivity of electrochemical gas sensors will change as time passes regardless of whether sensor has been used or not 4 Mounting of sensors Electrode pins must be connected correctly to ensure operation If a thermistor is used for temperature compensation it must be located near the sensor and away from heat sources such as transformers The 4 can be mounted in any orientation NE4 NH3 connection pins cannot be soldered as excess heating may cause the deformation of the housing and eventually leakage of electrolyte 5 Calibration and gas testing Calibration of detectors or densitometers should be done after the output value has been stab
6. offset types e g OP90 or similar e Some sensors require temperature compensation circuitry A simple compensation network can be incorporated into this circuit by replacing RG with a thermistor Typically this is a NTC thermistor that has 3435K of B constant adjusting the output accuracy to within 10 in the range of 10 C 50 C Any thermistor with a B constant around 3500K and resistance value Res of 10 KQ can be used Alternatively temperature compensation may be undertaken using software lookup tables NE4 NH3 Manual issue 4 Sept 2015 page 13 of 16 The circuit Nemoto employs for all its internal testing of NE4 NH3 is shown below Qut put Vol t age TH NIC Therm st or R 3435k 1O3AT I shi zuka El ectroni c Cor p Nemoto recognises that the companies who use its gas sensing devices are themselves experts in circuitry design often with more expertise than Nemoto in this area The information given here is hence for initial guidance only and Nemoto does not insist that instrument designers reproduce our circuitry guidance precisely If the instrument designer deviates from this guidance significantly however Nemoto advises that we should be consulted to ensure that the proposed circuit design will function correctly Failure to adhere to the
7. recommended circuitry outlined in this document without consultation with Nemoto may result in the suspension of the warranties which apply to the device GENERAL NOTES ON HANDLING MANUFACTURE AND INSTRUMENT DESIGN 1 Long term drift of gas sensitivity All electrochemical gas sensors lose sensitivity over time due to small changes on the surface of the working electrode reducing its oxidation capability To reduce this the NE4 NH3 uses a newly developed electrode catalyst that will not deteriorate by more than 596 year Typically these changes are limited to less than 596 but we recommend that this deterioration should be taken into account when designing application circuits SPECIAL NOTE Unlike other gas sensors of this type Ammonia sensors have an active reagent contained within the sensor which is slowly consumed by the sensor when it is exposed to ammonia The lifetime of the sensor in service is therefore somewhat governed by the eventual consumption of this reagent Nemoto has carefully designed the NE4 NH3 to ensure that there is enough of this reagent to last for at least 2 years of operation in the vast majority of gas detection applications where the sensor will not be exposed to ammonia unless a leak or other hazardous situation arises In applications where the sensor is likely to be exposed to a constant background level of ammonia or very frequently exposed to ammonia the lifetime of the sensor could be shorter than spe
8. 4 10 9 Takaido Higashi Suginami ku Nemoto Sensor Tokyo 168 0072 Engineering pia Company Lid Web www nemoto eu E mail sensor2 nemoto co jp Technical Information and User Manual NE4 NH3 Electrochemical Ammonia NH3 Gas Sensor For Industrial Applications Apart from pages 5 and 6 Specification and Dimensions sections the data in this document does not constitute a specification but is intended as a guide informing the instrument designer of the performance characteristics of the sensor which were observed by Nemoto Sensor Engineering scientists It should be read in conjunction with the official datasheet for the device which includes the full technical specification for the NE4 NH3 Gas Sensor Nemoto Sensor Engineering Co Ltd has a policy of continuous development and improvement of its products As such the specification and data outlined in this document may be changed without notice NE4 NH3 Manual issue 4 Sept 2015 A Nemoto amp Co Ltd was established in 1941 and continues to develop unique technologies for Safety Security and Health markets worldwide Using our unique experience of fine chemical preparation and printing we were able to enter the gas sensor market in 1979 with a range of high quality hot wire type sensors pellistors Nemoto is now one of the world s leading manufacturers of chemical sensors and has so far delivered over 30 million devices to the market INTRODUCTION As a result of th
9. Hs uA 5 18 0 00 i 8 Tolerance to Hydrogen The following table shows the zero and sensitivity change following an exposure to 500ppm Hydrogen for 10 hours The gas concentration used for testing was 100ppm Before exposure After exposure Sensitivity Zero offset in air Sensitivity to Zero offset in air Sensitivity to variation ratio uA 100ppm NHs uA uA 100 NHs uA 9 Tolerance to Silicone vapours The following table shows the zero and sensitivity change following an exposure to 200 HMDS HexaMethylDiSiloxane vapour for 120 minutes The gas concentration used for testing was 100ppm Before exposure After exposure Sensitivity Zero offset in air Sensitivity to Zero offset in air Sensitivity o Variation ratio 100ppm NHs uA 100ppm NHs uA NE4 NH3 Manual issue 4 Sept 2015 page 12 of 16 NOTES FOR CIRCUIT DESIGN The basic measuring circuit for all 3 electrode electrochemical gas sensors is shown below e Inthis arrangement the output voltage Gas Concentration ppm x Cell Output A x Re Q e So if Rais 100k cell output is 40nA ppm and gas concentration is 100ppm then VOUT 10 x 700x109 x 100x103 0 40V e Hiis the cell load resistor typically 5 500 Speed of response can be increased by reducing the value of Ri but signal noise may be increased as a consequence The recommended values are shown on sensor datasheets e Amplifiers should be high quality precision low input
10. cified Please contact Nemoto for further guidance NE4 NH3 Manual issue 4 Sept 2015 page 14 of 16 A Due to the hygroscopic nature of the electrolyte used in electrochemical sensors moisture is absorbed from or released to the surrounding atmosphere In high humidity moisture is absorbed causing an increased sensitivity In low humidity moisture is released back to the atmosphere and the sensitivity decreases Conventional electrochemical gas sensors show annual variation of gas sensitivity as much as 10 20 2 Environmental effects on gas sensitivity The 4 utilises an advanced electrolyte management design and combined with the unique electrode catalyst structure these changes can be greatly reduced Under normal operating conditions gas sensitivity should change by no more than 5 of the output value The NEA4 NH3 is designed so that all changes due to moisture uptake release are completely reversible If the gas intake area of the sensor is blocked with water drops or other liquid gas cannot enter the sensor The NE4 NH3 is fitted with an integral hydrophobic barrier to prevent this but we recommend the use of additional membrane barriers if the sensor in highly condensing RH conditions NHs gas is slightly less dense lighter than air In a typical safety related application detecting devices should hence be installed around least 5ft from the floor and preferably at higher level if possible However
11. ctrodes may be measured as a nA level current signal proportional to the ppm concentration of Ammonia The reference electrode maintains the healthy operation of the cell It is surrounded by electrolyte sees no gas and no current is allowed to be drawn from it Its electrochemical potential hence always remains constant at a level known as the rest air potential and this is used to regulate the potential of the working electrode regardless of the current it is generating during operation The use of a reference electrode in this way i e three electrode operation helps to extend the working range of the sensor improves linearity and results in a number of performance benefits compared with similar sensors working with 2 electrodes only NE4 NH3 Manual issue 4 Sept 2015 page 3 of 16 A FEATURES Electrochemical gas sensors have the following superiority to conventional semiconductor type and hot wire type gas sensors Linear output in proportion to gas concentration High reproducibility Highly gas specific Unaffected by humidity Stable output for long periods Low power consumption because no heater is used can be battery operated Small and lightweight can be used in portable devices No mechanical structure so highly resistant to shocks and vibrations The NE4 NH3 has been developed from our accumulation of technologies in production of hot wire type gas sensors long research experience into catalysts fine print
12. eparated by an acidic aqueous electrolyte housed within a plastic PPO enclosure Gas enters the cell via a gas phase diffusion barrier An electrolyte reservoir ensures an excess of electrolyte is available at all times and the sensor is vented to ensure that the internal and external pressure of the sensor is always in equilibrium In operation gas enters the cell via the capillary and filter and comes into contact with the working electrode Any Ammonia present undergoes an oxidation reaction The oxidation reaction converts the Ammonia into Nitrogen Which is simply expelled into the atmosphere through the capillary Hydrogen lons H Which are taken into the electrolyte Electrons e which are removed by the external circuit via a metal strip in contact with the working electrode which creates a small nA electric current in the metal strip The reaction at the working electrode is balanced by a reciprocal reduction reaction at the counter electrode using Oxygen from the surrounding atmosphere 4H 4e 2H2O The electrons consumed in this reaction are supplied by the external circuit via a metal strip in contact with the counter electrode Thus Hydrogen ions and electrons are generated at the working electrode whilst Hydrogen ions and electrons are consumed at the counter electrode By connecting the working and counter electrodes together via a special circuit the flow of electrons between the two ele
13. ilized in clean air Evaluation of gas sensitivity should be made in clean humidified air When a test gas is blown directly to the gas intake area higher gas sensitivity may be observed It is therefore best to test and calibrate gas detection instruments and sensors in diffusion mode This can be achieved by using a suitable test housing where a low flow rate is used lt 11 and where the air is agitated to ensure equal gas diffusion throughout Note that Nemoto s own internal testing systems place the sensor in a large chamber with the gas introduced by injection The chamber includes a fan which gently agitates the gas inside the chamber to ensure the test gas is NE4 NH3 Manual issue 4 Sept 2015 page 15 of 16 A fully mixed with the air and does not stratify in the chamber In this way Nemoto s own testing very closely simulates the action of the sensor in a typical application Other methods including the use of flow through hoods and pumped sampling assemblies may of course be used by instrument manufacturers but it should be recognised that the method used to expose the sensor to test gas will have a small effect on the accuracy and repeatability of the results obtained and the correlation of these results with Nemoto s own routine QA test results 6 Other Unless otherwise advised by Nemoto voltage should not be supplied directly to the electrode pins Do not bend the pins Do not apply more than 5
14. ing and assembling of sensors The NE4 NH3 is small and less expensive but has high sensitivity long life and leak free performance even under severe operating conditions Air vent The electrolyte used for chemical sensors is very hygroscopic i e it has affinity for water and its volume varies depending on ambient temperature and humidity This variation causes pressure inside the sensor to rise and fall In the worst case the electrolyte may leak out of the sensor and damage the circuitry around it To prevent this the NE4 NH3 utilizes an air vent capability This maintains equilibrium between internal and external pressures and allows the sensor to be used in any orientation and under high temperature and humidity conditions NE4 NH3 Manual issue 4 Sept 2015 page 4 of 16 SPECIFICATIONS 40 12 nA ppm NHs Zero offset in clean air MEN lt 10ppm equivalent Repeatability Same day measurement 10 Zero offset 10 ppm equivalent year Long Term Stability Sensitivity to NH3 2 signal month Temperature 5 Zero offset swing lt 15 30 C to 50 C In Service 30 C to 50 C Temperature range Recommended in Storage 0 C to 20 C 15 90 RH non condensing 15 9096 RH non condensing service resistor Recommended maximum storage time Warranty GEIS 12 months workmanship or materials In Service Humidity range Recommended
15. r recommended circuit as the conversion is done through a resistor of 10 KO Response time Too This is the time taken to reach 90 of the maximum output value in clean air Repeatability This is the maximum variation of output signals when tests are repeated under the same measuring conditions temperature humidity gas concentration etc The repeatability of NE4 NH3 is 2 and this means that all of the test results would fall in the range of 90 110 Temperature dependence All electrochemical sensors are affected by changes in the ambient temperature and the output increases as the ambient temperature rises This is caused by the rate of oxidation reaction on the surface of the catalyst the dispersibility of the gas in the capillary and the thermal effects on the mobility of ions in the electrolyte This temperature dependency can be compensated relatively easily by using a NTC thermistor NE4 NH3 Manual issue 4 Sept 2015 page 16 of 16
16. rated in bench tests in a controlled clean environment In service in a real application the long term stability will also be dependent on the environmental conditions of the application NE4 NH3 Manual issue 4 Sept 2015 page 8 of 16 A TOLERANCE TO ENVIRONMENTAL EXTREMES 1 Tolerance to Humidity Variations The following graph illustrates the zero offset variation of the sensor when exposed to large and frequent sudden swings in humidity The Atmosphere was cylcled from close to 0 RH to 90 RH every 10 minutes The sensors zero offset does respond slightly to these humidity transients the swing is a transient effect quickly returning to its previous value and was limited to lt 5ppm equivalent 1 0 a LL LL LE LE EL LLL tt LLL fi fi f tt pe pe en eee Ae 401 mE Output JLA e pi ttt ty ptt LL TP ett PE l l 1 0 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 Time min 2 Tolerance to temperature and Humidity extremes bd High Temperature Low Humidity The following graph illustrates the signal output stability for a sensor exposed to 50 C at close to 096 RH over 10 000 hours The NHs concentration used was 100 in air 14096 12096 d 5 10096 E E 80 60 amp 40 20 0 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 Time h NE4 NH3 Manual
17. ree years development at our Tokyo R amp D centre we released our first electrochemical gas sensor in 2000 The NE4 NH3 Gas Sensor is a 3 Electrode electrochemical gas sensor designed for the detection and measurement of Ammonia in the range 0 100ppm in a wide range of industrial and commercial safety applications By adhering to industry standards for size and connection orientation the NE4 NH3 can be retrofitted easily to existing product designs By using our experience of design for manufacture and our high volume production facilities in Japan and China we have successfully reduced the cost of the NE4 NH3 whilst being able to maintain the highest performance quality NOTE Nemoto offers 3 variants of the NE4 NH3 series sensors Signal Output Standard sensor for occupational Nees bcd id exposure monitoring of toxicity levels NE4 NH3 1000 0 1000 ppm 8 nA ppm vais with an extended measuring For monitoring in the explosive LEL range for example the protection of SOU etn Eo ain refrigeration plants from explosive levels of gas NE4 NH3 Manual issue 4 Sept 2015 page 2 of 16 PRINCIPLES OF OPERATION PTFE Membrane N2 Electrolyte Ht Counter electrode Output NH3 Rr Working electrode Reference electrode Potentiostat The 4 consists of porous noble metal electrodes s
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