Dynasonics TFX Ultra Transit Time Flow Meters - Manual (Page 61)

Flow at 4 mA / 0 Hz
Flow at 20 mA / 1000 Hz
The Flow at 4 mA / 0 Hz and Flow at 20 mA / 1000 Hz entries are used to set the span of the 4-20 mA analog output and
the frequency output on flow only versions. These entries are volumetric rate units that are equal to the volumetric units
configured as rate units and rate interval discussed on page 44 .
For example, to span the 4-20 mA output from –100…100 gpm with 12 mA being 0 gpm, set the Flow at 4 mA / 0 Hz and Flow
at 20 mA / 1000 Hz inputs as follows:
Flow at 4 mA / 0 Hz = –100.0
Flow at 20 mA / 1000 Hz = 100.0
If the meter is a flow only model, this setting would also set the span for the frequency output. At –100 gpm, the output
frequency would be 0 Hz. At the maximum flow of 100 gpm, the output frequency would be 1000 Hz, and in this instance a
flow of zero would be represented by an output frequency of 500 Hz.
Example 2 – To span the 4-20 mA output from 0 …100 gpm with 12 mA being 50 gpm, set the Flow at 4 mA / 0 Hz and Flow at
20 mA / 1000 Hz inputs as follows:
Flow at 4 mA / 0 Hz = 0.0
Flow at 20 mA / 1000 Hz = 100.0
For the meter, in this instance, zero flow would be represented by 0 Hz and 4 mA. The full scale flow or 100 gpm would be
1000 Hz and 20 mA and a midrange flow of 50 gpm would be expressed as 500 Hz and 12 mA.
The 4-20 mA output is factory calibrated and should not require adjustment. If small adjustments to the DAC (Digital to
Analog Converter) are needed, for instance if adjustments due to the accumulation of line losses from long output cable
lengths are required, the Calibration 4 mA and Calibration 20 mA can be used.
Calibration 4 mA — 4 mA DAC Calibration Entry (Value)
Calibration 20 mA— 20 mA DAC Calibration Entry (Value)
The Calibration 4 mA and Calibration 20 mA entries allows fine adjustments to be made to the “zero” and full scale of the 4-20
mA output. To adjust the outputs, an ammeter or reliable reference connection to the 4-20 mA output must be present.
OTE:
N
Calibration of the 20 mA setting is conducted much the same way as the 4 mA adjustments.
OTE:
N
The Calibration 4 mA and Calibration 20 mA entries should not be used in an attempt to set the 4-20 mA range.
Utilize Flow at 4 mA / 0 Hz and Flow at 20 mA / 1000 Hz detailed above for this purpose.
4 mA Calibration Procedure:
1. Disconnect one side of the current loop and connect the ammeter in series (disconnect either wire at the terminals
labeled 4-20 mA Out or Signal Gnd).
2. Using the arrow keys, increase the numerical value to increase the current in the loop to 4 mA. Decrease the value to
decrease the current in the loop to 4 mA. Typical values range between 40…80 counts.
3. Reconnect the 4-20 mA output circuitry as required.
20 mA Calibration Procedure:
1. Disconnect one side of the current loop and connect the ammeter in series (disconnect either wire at the terminals
labeled 4-20 mA Out or Signal Gnd).
2. Using the arrow keys, increase the numerical value to increase the current in the loop to 20 mA. Decrease the value to
decrease the current in the loop to 20 mA. Typical values range between 3700…3900 counts.
3. Reconnect the 4-20 mA output circuitry as required.
4-20 Test — 4-20 mA Output Test (Value)
Allows a simulated flow value to be sent from the 4-20 mA output. By incrementing this value, the 4-20 mA output will
transmit the indicated current value.
BASIC TAB
Page 61 March 2014