We found many problems in NO2 sensors. Can we plz provide the informations

1. What is RL range we should use.
2. Across which resister (Rs or RL) the op voltage is being taken which is going to ADC.
2. As a convention & like other sensor, across RL op voltage should be taken.
3. Now the range of R0 is about 0.8 kohm to 8 Kohm. Setting a 50 Kohm Load will lead the op voltage to the supply that is 1.8 V when the NO2 concentration is 0 ppm.
But surprisingly the op voltage is coming -0.0225806450 v at RL 50 Kohm
Then for testing purpose I set the RL 100ohm & got again a surprise that now the op is 1.8774193763 voltage. at RL=100ohm

Testing with 10Kohm
Result -0.0225806450 v at RL=10Kohm

in all the cases NO2 is 0 ppm
CODE:

void setup()
{
USB.begin();
SensorGas.setBoardMode(SENS_ON);
SensorGas.configureSensor(SENS_SOCKET2B, 1, 10000);
}

void loop()
{

SensorGas.setSensorMode(SENS_ON, SENS_SOCKET2B);
delay(300000);
float NO2_value = SensorGas.readValue(SENS_SOCKET2B);
SensorGas.setSensorMode(SENS_OFF,SENS_SOCKET2B);
USB.print("SENSOR number 9 - ");
USB.println(NO2_value);

}






Plz resolve this issue

Hi biprangshu,

the best choice for RL would be to match the resistance value of the sensor in normal conditions, in air it would be between 0.8 and 8 kohms (average is in 2.2kohms).

Your point2 is correct, the voltage measured is that on the load resistor, but take into account that the measurement range is not between 0.8 and 8 kohms, that is the range that the resistance in air of the sensor may take (I'm not sure if that is what you meant, I prefer to clarify it).

The values you expect are correct, but you are configuring the sensor wrong, the load resistor's value must be specified in kiloohms, not in ohms. Try to correct it and let us know how did it work.

Regards.

Thanks for the information. but tell me 1 thing If I set the RL =10K with gain 1 & 0 ppm No2 then op voltage should be gretter than 0.5 Volt where it is coming only 0.02258 V & with RL=100 ohm it should be 0.2volt where it is coming 1.8Volt. This is main problem I am getting

Hi biprangshu,

as I said before, you are not configuring properly the load resistor. Since you are setting its value in ohms instead of kiloohms, the resistance is out of range and the result is not coherent.

Please correct your code and tell us if your problem persists.

Regards.

Plz ignore my replye posted on Wed Apr 06, 2011 3:15 pm. Thank again, For the information . Now its working fine. The mistake I was doing is I put 10000 to set 10Kohm load resistance, bcoz I thought that I need to put the RL in ohms.Plz update your gas sensor board document with sample RL value & format of writiing.
Regards
Biprangshu

Hi,

Kindly look at my gas values (Co2, co, NH3, CH4, No2) from XBee:

~j€}3¢@i8½+R#Vx#,NodeID,1,Count,6,Time,13:32:40,Temp,23,X,36,Y,-10,Z,1052,Co2,464,Co_H2,0,NH3_H2S,0,CH4H~}3¢@i8½+R
Vx2,1364,No2,k

~j€}3¢@i8½*R#Vx#,NodeID,1,Count,7,Time,13:33:6,Temp,24,X,36,Y,-10,Z,1051,Co2,474,Co_H2,0,NH3_H2S,0,CH4H2~}3¢@i8½+R
Vx,1341,No2,1q

~j€}3¢@i8½+R#Vx#,NodeID,1,Count,8,Time,13:33:33,Temp,24,X,36,Y,-10,Z,1052,Co2,483,Co_H2,0,NH3_H2S,0,CH4H}3~}3¢@i8½+R
Vx2,1322,No2,q

~j€}3¢@i8½*R#Vx#,NodeID,1,Count,9,Time,13:33:59,Temp,25,X,36,Y,-10,Z,1052,Co2,487,Co_H2,0,NH3_H2S,0,CH4H~}3¢@i8½*R
Vx2,1312,No2,s

~j€}3¢@i8½,R#Vx#,NodeID,1,Count,10,Time,13:34:25,Temp,25,X,36,Y,-10,Z,1052,Co2,493,Co_H2,0,NH3_H2S,0,CH4-~}3¢@i8½,R
VxH2,1296,No2J

~j€}3¢@i8½+R#Vx#,NodeID,1,Count,11,Time,13:34:51,Temp,26,X,36,Y,-10,Z,1051,Co2,496,Co_H2,0,NH3_H2S,0,CH4+~}3¢@i8½+R
VxH2,1287,No2K

~j€}3¢@i8½#R#Vx#,NodeID,1,Count,12,Time,13:35:17,Temp,26,X,35,Y,-8,Z,1051,Co2,529,Co_H2,0,NH3_H2S,0,CH4H~}3¢@i8½%R
Vx2,1341,No2,v

QUESTIONS:
1) Please why am I getting alphabets q, s, v, etc. as my No2 gas values?

Look at the sketch of my code, which is transmitting the gases:
----------------------------------------------------------------------------------------------------------------------
uint8_t PANID[2]={0x12,0x34};
char* KEY="WaspmoteKey";

packetXBee* paq_sent;
int8_t state=0;
long previous=0;
//char* data="WaspMote board 5!";
char data[200];
int g=0;
int temperature=0,x_acc=0,y_acc=0,z_acc=0,co2=0,co=0,NH3=0,CH4=0;
int No2=0;
int node_id,trans_count;

...........
............

/* Setting up the Gas Board */
SensorGas.setBoardMode(SENS_ON); //turns on

SensorGas.configureSensor(SENS_CO2,1); //Setting up the CO2 sensor
SensorGas.setSensorMode(SENS_ON, SENS_CO2);
XBee.println("Co2 Configured");

SensorGas.configureSensor(SENS_SOCKET4B, 1, 10); //Setting up the co & H2
XBee.println("co/H2 Configured");

SensorGas.configureSensor(SENS_SOCKET3C, 1, 8); //Setting up the NH3 & H2S
XBee.println("NH3/H2S Configured");

SensorGas.configureSensor(SENS_SOCKET2A, 1, 3); //Setting up the CH4 & H2
SensorGas.setSensorMode(SENS_ON, SENS_SOCKET2A);
XBee.println("CH4/H2 Configured");

SensorGas.configureSensor(SENS_SOCKET2B, 1, 10); //Setting up the No2
SensorGas.setSensorMode(SENS_ON, SENS_SOCKET2B);
XBee.println("No2 Configured");
......
.......

/*Take readings from the gas board*/
co2 = (int)(1000*SensorGas.readValue(SENS_CO2)); //reading co2
co = (int)(1000*SensorGas.readValue(SENS_SOCKET4B)); //reading co and H2
NH3 = (int)(1000*SensorGas.readValue(SENS_SOCKET3C)); //reading NH3 and H2S
CH4 = (int)(1000*SensorGas.readValue(SENS_SOCKET2A)); //reading CH4 & H2
No2 = (int)(1000*SensorGas.readValue(SENS_SOCKET2B)); //reading No2
//pressure = (int)(1000*SensorGas.readValue(SENS_PRESSURE)); //reading pressure

/* Copying readings into data array */
sprintf(data,"#,NodeID,%d,Count,%d,Time,%d:%d:%d,Temp,%d,X,%d,Y,%d,Z,%d,Co2,%d,Co_H2,%d,NH3_H2S,%d,CH4H2,%,No2,%,\n\n",node_id,trans_count,RTC.hour,RTC.minute,RTC.second,temperature,x_acc,y_acc,z_acc,co2,co,NH3,CH4,No2);

----------------------------------------------------------------------------------------------------------------------

Hope to receive from you urgently.
Thanks.

Answered in this post:

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