FTB700-T INSTRUCTIONS
Page 9
omega.com
SETTINGS AND CALIBRATION
Setting Frequency
The FTB700-T converts a train of off/on pulses from the
flow sensor into a continuous milliAmp signal that ranges
from 4 mA at zero flow to 20 mA at the desired maximum
flow. The desired maximum is determined by the user and
entered as a frequency as follows:
1.
Decide what flow rate should represent the top of
the scale. This is ordinarily the maximum expected
flow, or a value just above it, in gallons per minute.
2. Locate the K-factor of the flow sensor (found on
the meter or fitting. The K-factor is the number of
pulses the flow sensor produces per gallon of flow.
3.
Calculate frequency, using this formula:
K-Factor x
Top Flow (GPM)
= Frequency
60
4.
Enter the frequency using the four rotary Frequency
switches. Note the decimal point between the third
and fourth switches.
Setting Averaging Time
For most applications, this step can be ignored, as the
standard setting will work fine. However, when a particularly
steady output signal is desired, or in large pipe, a larger
averaging period may be desirable. Note however that
the averaging period requires a tradeoff, since a longer
averaging period implies a slower response time. If steady
signal is more important than fast response, increase the
averaging time as desired. See the diagram below for the
switch positions and their corresponding times.
Checking Calibration
Normally it should not be necessary to check calibration,
since the digital design of this unit virtually eliminates drift.
However, there are two types of calibration check that can
be performed. Look at the diagram below to locate the 4
and 20 mA force switches. To force the 4 mA output, put
its switch in the up position. Check the current output at
the Power terminals, and if necessary trim to 4.00 mA using
the appropriate trimpot. Return the switch to the down
position, and repeat the process with the 20 mA switch.
Power
Sensor
4-20 mA
UP
DOWN
L
R
FTB700-T
Frequency
0
98
7 6 5 4
3
2
1
0
98
7 6 5 4
3
2
1
0
98
7 6 5 4
3
2
1
0
98
7 6 5 4
3
2
1
Power
Sensor
4-20 mA
4mA Adjust
Force 4 mA
Force 20 mA
20 mA Adjust
S
FTB700-T
Frequency
0
9
8
7 6 5 4
3
2
1
0
9
8
7 6 5 4
3
2
1
0
9
8
7 6 5 4
3
2
1
0
9
8
7 6 5 4
3
2
1
Setting Frequency Example
1.
In an installation with an estimated maximum
flow rate of about 150 GPM, a flow rate of 170
GPM is selected as the full-scale maximum, the
flow at which the current loop will register 20
mA.
2. In this example, the K-factor (found on the
meter or fitting, or in the manual) is “K =
54.50”.
3.
Calculate the frequency as:
54.50 x 170 = 154.42
60
4. Rounding to one decimal point, enter 154.4 on
the rotary switches by turning the rotary switch
pointers to the desired digits.
Power
Sensor
4-20 mA
FTB700-T
Frequency
0
98
7 6 5 4
3
2
1
0
98
7 6 5 4
3
2
1
0
98
7 6 5 4
3
2
1
0
98
7 6 5 4
3
2
1
1
5
4 . 4
Switch Position
Seconds
L
R
2
down
down
4
down
up
8
up
down
16
up
up
