This site runs best with ActiveX enabled on computers running Microsoft Internet Explorer. Other technical articles on die casting by Bob McClinticĮ-mail: Bob McClintic and Associates: 2017 Second, by training your personnel in the use of the tools and methodology.Ĭlick the following for information on consulting and training services offered by McClintic & Associates.
If you would like to learn how to reduce your PPM while increasing profits I can help.įirst by demonstrating a systematic and scientific approach to design and manufacturing in your facility. If you don't measure it you can not control it. It is the result of careful planning, design, and execution. Quality can not be inspected in after the fact. We can now control the process in order to control the quality. The monitoring and measurement systems we have today have paved the way for improved quality. Insanity is doing things the same way we've always done them and expecting different results. Impossible? Yes if you are still using the same manufacturing methods which were responsible for the 5 or 10% scrap you used to accept.Ī friend of mine had the following quotation on his wall: Way, one bad part per day! Notice I did not say one bad part per day per That means that you would be allowed 25 pieces for everyġ,000,000 pieces or 250 defective parts per year. Let's assume your customers requirementsĪre 25 PPM. Like most companies, your plant operates around 5 days a week, 50 weeks Say, you produce 10,000,000 parts per year for your customer. To calculate: For example, let's say you had 25 pieces defective in a shipment of 1,000 pieces. Now the rate for most automotive components is targeted at 25 PPM or 0.0025% There was a time when you were considered a pretty good supplier when your defect rate was less than 1%, (10,000 PPM), then the expectation was increased to 0.1% or 1,000 PPM. Most boards use a 2 kilo-ohm resistor for R2.PPM (Parts per million) is a measurement used today by many customers to measure quality performance.ĭefinition: One PPM means one (defect or event) in a million or 1/1,000,000
Thus, RS can be determined if the series resistor R2 from the schematic is known. RS is the sensor resistance and forms a voltage divider with the resistor R2 (see schematic diagram above). Since by definition, R0 is the resistance of the sensor in clean air, then only RS varies for every gas. This varies between devices so there is a need for actual testing.įrom the log-log plot, we can see that RS/R0 is constant in air and is equal to 1. Or, the relationship between concentration in ppm and RS/R0 is now:īefore we can use this formula in a sketch, we need to determine R0 of the MQ-7 sensor first. The encircled two points are approximated to be: We can select two points on the plot, as shown: Where F1, x1, and F0, x0 are any two points in the plot.
The function of a line in such a plot is given as To get an EC value, multiply the ppm reading by 2 and divide by 1000.
We are only interested in the blue line on the plot which gives the CO concentration. How do you calculate EC from PPM To obtain an approximate sodium chloride TDS value, multiply the EC reading (in milliSiemens/cm) by 1000 and divide by 2. We can convert the voltage reading to ppm if we look at the characteristic curve above, which is a log-log plot. Meanwhile, the AOUT pin gives varying voltage representing the CO concentration. The threshold can be varied by adjusting the trimmer on the breakout board which is Rp in the schematic. One is through the DOUT pin which gives a high when the concentration threshold is reached and low otherwise. There are two ways to read the output from the MQ-7. This schematic diagram is the same as with the MQ-3 alcohol sensor and MQ-6 LPG sensor. This breakout board is more convenient as it converts resistance variations to voltage variations. We will use this graph later when we create our code.įor this tutorial, I will be using the MQ-7 breakout board which has four output pins as shown:
Rs is the resistance of the sensor in target gas while R0 is the resistance in clean air. Here is its sensitivity characteristic curve: Introduction to MQ-7 Carbon Monoxide SensorĪccording to its datasheet, the MQ-7 carbon monoxide sensor detects 20 to 2000 ppm of CO in air. Since this gas is considered toxic to humans at certain levels, concentration of CO is used to determine the air pollution in a given area. The MQ-7 carbon monoxide sensor is especially designed to be sensitive to carbon monoxide (CO) gas which is emitted by vehicles, factories, etc.