What is the difference in gain between the ML140 Spirometer and ML311 Spirometer Pod?

The pressure sensitivity of the spirometer is 0.5 V/inch H20.

For Spirometer pods with serial numbers, the pressure sensitivity of the pod is 10 mV/inch H20 and there is a gain in the pod circuitry of (50 000/680 + 1) which corresponds to 75, such that 10 mV/inch corresponds to an output of 0.75 V/inch H2O. The pod is further complicated by a ratiometric span. Output for the transducer is typically 40 mV for FS corresponding to 0-4 inches H2O when the supply voltage is 12 VDC. The pod uses a 10V rail which reduces the theoretical output to around 0.6 V/inch H2O. The difference between these values makes the whole thing a lot more interesting.

The signal ratio between the pod and the spirometer is around 1.25 when both are recording the same pressure difference. Spirometer pods with serial numbers greater than > PSP 600 have the same gain as the spirometer of 0.5 V/inch H20.

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