Sensor MQ7 I dont understand how....

I know and I readed many posts about this sensor. MQ7 Co meter. I buyed one and I test it but I dont understand somethings about how this work. http://www.ebay.es/itm/181266971723?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649 This one have two output, one digital and one analogic. work with 5V Dc.The board have one operational amplifier LM393 and a led- When I readed the datasheet of the sensor MQ-7 I think that I must power it with 5VDC for 60 seg and 1,4 V DC for 90 seg. Well, I dont know when I must read the analogic value.. Is the OK value after this time 60+90 seg , in the second 60 seg period? The sensor analog output is real value when power is 1,4V Dc or when it is 5 VDC. Is the digital pin low when sensor value is ready for be readed, or what is the use of this digital pin? When and why is the led ON ? I found similar sensor circuit board that have only analog output,but I think thats dont work ins similar way. When can I found a library or example for this circuit board with LM393 and led....? My last question, how many ppms of CO can I meter with this sensor, 1000ppms or 10000ppms? I was two days Reading of this sensor and I dont understand, there are many question but I need use one for check my motorcycle, I did a equipement for meter my motorcycle paramenter,vaccum of carburators, presión of tires, batery volts, rpms...and CO meter....but this is my problema for finished the equipment. Thank you so much and excuse my bad english.

Do you have a datasheet for the sensor?

also, have you thought about using a wide band sensor instead of CO sensor?

http://www.aemelectronics.com/wideband-air-fuel-systems-15/digital-wideband-air-fuel-gauge-25/

Yes this is datasheet of the sensor but I dont have scheme of the module only of sensor MQ7. This is datasheet https://www.sparkfun.com/datasheets/Sensors/Biometric/MQ-7.pdf I dont need meter the % fuel air, I only need meter CO and no CO2, because the technical Inspection of motorcycles in Spain only test %CO. This must be less to 0,2% Thanl you very much

On this page

http://thesis.jmsaavedra.com/prototypes/technology/mq-7-carbon-monoxide-sensor-breakout/

you'll find a drawing explaining the values you may read from the sensor in the different heating periods. The circuit found there can be read using this library (http://thesis.jmsaavedra.com/prototypes/software/mq-7-breakout-arduino-library/).

Hope this helps.

Yes I know this post, I readed all and I dont understand when is the best time for take a simple, when the Volts are 1,4 or 5 V, When is finished the 60 seconds time or when is finished 90 seconds times. Thank you again

I was testing.....there are a problem when I try use PWM for do 1.4 V and take a sample. the pwm make the power current no good and sample is no good too. It is necesary use a filtred tensión for do it good. The relation in PPMs and sample value it is very dificult to do.

When is finished the 60 seconds time or when is finished 90 seconds times.

If you look at the example code of the library you can see that you only get meaningful values while not heating (means 1.4V). I would measure the value during the whole period and returning the average of all readings. An alternative would be to use the last reading just before you starting heating with 5V again.