CS115 Barometric Pressure Sensor

Once the CS115 is turned on one minute before every hour, and the correct measurement is made, it is then copied into the current variable called "Pressure". The sensor is then turned off immediately following the measurement. In this example, the CR5000 measures the CS115 once every hour while measuring other sensors at 10 Hz.

In Example 5, the 21X turns on the CS115 one minute before the top of the hour, and on the hour it measures the CS115 using the pulse count instruction. The execution interval should be set at 1 second, and the configuration code for Pulse instruction (P3) should be set at 24, Low Level AC, 16-bit, Output in Hz. When this option is selected, two adjacent 8-bit pulse counters (Pulse Input channels 1 and 2) are combined into one input channel (Pulse Input channel 1) to form a 16-bit accumulator. Therefore, Pulse Input channel 2 cannot be used. You can also choose to use Pulse Input channel 3, in which case Pulse Input channels 4 will be combined with Pulse Input channel 3 to form a 16-bit accumulator. In this mode, the 21X’s execution interval must be less than one minute. If the execution interval is longer than one minute, you will get an error, because the 16-bit pulse accumulator will overflow counting the signal from the CS115 when it outputs close to 1100 Hz (1100 mb of barometric pressure).

In the example programs above, the pressure is reported in millibars (mb). To report pressure in different units, multiply the measured pressure by the appropriate conversion factor using the P37 (Z=X*F) instruction for the CR500, CR510, CR10(X), CR23X, 21X and CR7, or by adding an expression for the CR5000 and CR9000. See Table 5-1 below for conversion factors.

TABLE 5-1. Conversion Factors for

Alternative Pressure Units

To Find

Multiply by

hPa

1.0

 

 

kPa

0.1

 

 

mm of Hg

0.75006

 

 

in of Hg

0.02953

 

 

psi

0.0145

 

 

atm

0.00099

 

 

torr

0.75006

 

 

6