Application Note

1.2

Application Note

1.2.1

RATE - Frequency Measurements

The Flow Indicator can be used as a basic frequency counter simply by inserting in the front panel

thumbswitches the value of one second or decimal equivalents. The gate time of one second will

transcribe the input signal into frequency directly in terms of cycles or pulses per second. A setting of

.100000 X1 is one second. One second may also be set by .010000 X10 or .001000 X100 or .000100

X1000. With a one second gate time, the readout displays directly in Hz (XXXXXX Hz). When using

settings other than 1 second, care must be exercised to mentally locate the decimal point. Starting

from a setting of .010000 X10, the display can be expanded in either direction simply by changing the

multiplier (.010000 X1 = XXX.XX KHz and .010000 X100 = XXXX.X Hz). Scaling of frequency readings

may be extended to the limits of the time base range. (See Specifications, Section I for limits.)

Normalized Rate

Normalized rate measurements are special cases of frequency measurement. Specific applications

include the quantizing and displaying of shaft rotational rates (tachometer) liquid flow rates (turbine

flowmeters) and speed indication of production line or conveyor belt systems. The CF-604 features

high input sensitivity which is compatible with the direct output of a variety of widely used

electromagnetic transducers.

The ability of a counter to vary its time base has greatly extended the usability of rate counters.

Proper adjustment of the time base makes possible direct readout in basic engineering units such that

troublesome conversions are completely avoided. This ability to read directly also avoids costly errors

in calculations and speeds identification of system problems by quick identification. Selecting the

proper gate time is the most critical factor in this type of counter. However, once one acquires an

understanding of what is occurring within the counter, normalized settings may be derived quite easily.

Normalized rate is accomplished by adjusting the gating interval of the counter so as to sample only

that portion of the input signal required to provide the proper display. If we have a sensor, for

example, delivering 100 pulses for each revolution of a shaft, then in order to read RPM, we only want

to display 1 for every 100 pulses received. With a rotational rate of 1 RPM and a gate time of 1

minute, the counter would obviously display 100.

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