Dynasonics TFX Ultra Transit Time Flow Meters - Manual (Page 32)

Frequency Output [Flow Only Models]
The frequency output is an open-collector transistor circuit that outputs a pulse waveform that varies proportionally with flow
rate. This type of frequency output is also know as a “Rate Pulse” output. The output spans from 0 Hz, normally at zero flow
rate to 1000 Hz at full flow rate (configuration of the MAX RATE parameter is described in detail in the flow meter configuration
section of this manual).
90-265 VAC
AC Neutral
Signal Gnd.
Control 2
Frequency Out
4-20 mA Out
Reset Total
10k
+V
1 2 3 4 O
N
Control 1 SW4 Closed
SW4 Open
Frequency Output
Figure 29: Frequency output switch settings
The frequency output is proportional to the maximum flow rate entered into the meter. The maximum output frequency is
1000 Hz.
OTE:
N When USB programming cable is connected, the RS485 and frequency outputs are disabled.
If, for example, the MAX RATE parameter was set to 400 gpm then an output frequency of 500 Hz (half of the full scale
frequency of 1000 Hz) would represent 200 gpm.
In addition to the control outputs, the frequency output can be used to provide total information by use of a K factor. A K
factor simply relates the number of pulses from the frequency output to the number of accumulated pulses that equates to a
specific volume.
For this meter the relationship is described by the following equation. The 60,000 relates to measurement units in volume/
min. Measurement units in seconds, hours or days would require a different numerator.
60,000
K factor
Full Scale Units
=
A practical example would be if the MAX RATE for the application were 400 gpm, the K factor (representing the number of
pulses accumulated needed to equal one gallon) would be:
60,000
150
400
Pulses Per Gallon
gpm
K factor = =
If the frequency output is to be used as a totalizing output, the flow meter and the receiving instrument must have identical K
factor values programmed into them to ensure that accurate readings are being recorded by the receiving instrument. Unlike
standard mechanical flow meters such as turbines, gear or nutating disk meters, the K factor can be changed by modifying
the MAX RATE flow rate value.
OTE:
N For a full treatment of K factors please see the APPENDIX of this manual.
There are two frequency output types available:
1. Turbine meter simulation – This option is utilized when a receiving instrument is capable of interfacing directly with a
turbine flow meter’s magnetic pickup. The output is a relatively low voltage AC signal whose amplitude swings above and
below the signal ground reference. The minimum AC amplitude is approximately 500 mV peak-to-peak. To activate the
turbine output circuit, turn SW4 OFF.
ALARM OUTPUTS
Page 32 March 2014