Wide range continuous diluter
View Patent ↗A wide range continuous diluter for diluting gases that contain small particles to allow subsequent measurement of the diluted gases with an instrument is provided. A dilution gas inlet receives a dilution gas, and a sample gas inlet receives a sample gas. A flow meter measures the sample gas flow rate. A mixer receives and mixes the dilution gas and the sample gas at a dilution ratio. An instrument flow outlet provides a well-defined flow into the instrument from the mixture flow. A make-up gas inlet is arranged to provide make-up gas into the mixture flow at a controlled rate. Because the dilution gas flows at a controlled rate and the mixture flows at a controlled rate, changing the flow rate of the make-up gas causes a responsive change in the sample gas flow rate, thereby allowing continuous adjustment and control of the dilution ratio when desired.
1. A wide range continuous diluter for diluting gases that contain small particles to allow subsequent measurement of the diluted gases with an instrument, the diluter comprising:
a dilution gas inlet for receiving a dilution gas at a controlled rate;
a sample gas inlet for receiving a sample gas;
a flow meter for measuring the sample gas flow rate;
a mixer connected to the dilution gas inlet and to the sample gas inlet for receiving and mixing the dilution gas and the sample gas at a dilution ratio, the mixer having an outlet for providing a mixture flow at a controlled rate;
an instrument flow outlet arranged to provide a well-defined flow into the instrument from the mixture flow;
a make-up gas inlet arranged to provide make-up gas into the mixture flow at a controlled rate; and
whereby changing the flow rate of the make-up gas causes a responsive change in the sample gas flow rate, thereby allowing continuous adjustment of the dilution ratio.
2. The diluter of claim 1 wherein the mixture flow rate is controlled by a critical flow orifice.
3. The diluter of claim 1 wherein the mixture flow rate is controlled by a mass flow controller.
4. The diluter of claim 1 wherein the dilution gas flow rate is controlled by a mass flow controller.
5. The diluter of claim 1 wherein the flow meter for measuring the sample gas flow rate comprises an orifice flow meter.
6. The diluter of claim 1 wherein the flow meter for measuring the sample gas flow rate comprises a plurality of differently sized orifice flow meters, and wherein the orifice flow meter applied to the sample gas flow depends on the dilution ratio.
7. The diluter of claim 1 further comprising:
a feedback control loop for controlling the dilution ratio by varying the make-up gas flow such that the dilution ratio tracks a desired value.
8. The diluter of claim 7 wherein the feedback control loop utilizes proportional/integral/derivative control.
9. The diluter of claim 7 wherein the feedback control loop is configured to track a constant dilution ratio.
10. The diluter of claim 1 wherein the flow into the instrument is a constant instrument flow.
11. The diluter of claim 1 wherein the flow into the instrument is a well-defined variable instrument flow.
12. The diluter of claim 1 further comprising:
a by-pass flow outlet upstream of the flow meter to reduce the residence time of the sample gas flow in a transfer line connecting the sample gas inlet to the sampling source.
13. The diluter of claim 1 further comprising:
a filter located upstream of the make-up gas inlet.
14. A method of using the wide range continuous diluter of claim 1 , the method comprising:
controlling the make-up gas flow rate to cause an outward flow from the sample gas inlet; and
obtaining the measurement from the instrument.
15. A method of using the wide range continuous diluter of claim 1 , the method comprising:
adjusting the make-up gas flow rate to cause a responsive change in the sample gas flow rate.
16. The method of claim 15 wherein the make-up gas flow rate is adjusted such that the dilution rate tracks a desired value.
17. The method of claim 16 wherein the desired value is a constant dilution rate.