Normalized Rate-continued - TM-9-4931-456-14-10019

1.2.1

Normalized Rate (Cont'd)

To achieve a reading of one, the gate time of one minute must be divided by 100. Therefore, in

1/100th of a minute one pulse would be registered by the counter which is the desired value for RPM

display. Since the counter gate is designated in seconds, it is necessary to convert the 1/100th of a

minute to seconds for proper insertion into the counter i.e., 60/100 seconds or .6 seconds.

The following steps and examples will illustrate the principle in more detail.

Step 1:

Determine the K factor or characteristics of the output signal from the sensor or transducer to

be used. (Tachometers, for example, deliver N pulses per revolution. Flowmeters typically

deliver N pulses per gallon, etc.) Most devices delivering pulses or cycles as a function of

rate may be used as inputs and the K factor is given by the manufacturer of the sensor used.

Step 2:

Decide on the final engineering units required in the display (RPM, gallons per minute, feet

per second, etc.).

Step 3:

Convert the time units contained in Step 2 to seconds as all time base calculations must be

in seconds for proper counter interpretation. This value then becomes T in the following

formula (i. e. RPM and GPM would require a T of 60 to convert minutes to seconds).

Step 4:

Determine the time base setting (t) by dividing the K factor into the T found in Step 3, t = T

Step 5:

Insert this number into the thumbswitches. The display will now read directly in the units

established in Step 2. Several examples will illustrate the procedure.

Example 1:

Reading RPM from a shaft encoder.

Step 1:

Tachometer K factor is 60 pulses per revolution.

Step 2:

Desired readout is revolutions per minute.

Step 3:

RPM requires a conversion factor of 60 to resolve one minute to 60

seconds; therefore, T= 60.

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