Badger Meter 106-255 User Manual

Bulletin 106-255

HOOK-UP INSTRUCTIONS – MODEL 106-255

SIGNAL CONDITIONER, MODULATED CARRIER, METER MOUNTED

APPLICATION

The Model 106-255 Meter Mounted Modulated Carrier
Signal Conditioner is intended for use with the wide
range Cox Series ANC and LFC Turbine Flowmeters.
The signal conditioner is designed to be mounted
directly to the flowmeter and when installed in this
way is contained in an explosion-proof housing. The
following describes the available options for
installation and connection to peripheral
instrumentation.

INSTALLATION

Figures 1A and 1B illustrate the most commonly used
methods for electrically interfacing to the signal
conditioner. Figure 1A is referred to as the TWO
WIRE INTERFACE while Figure 1B illustrates the
typical THREE WIRE INTERFACE. In both
instances, a regulated DC power source is required
as is some type of frequency meter or programmed
rate indicator, used to process or display the
flowmeter signal. The regulated DC power source
should provide an output of between 15 and 28 volts
DC with a minimum output current capability of 100
milli-amperes. Also, in either configuration the
flowmeter pick-off is connected directly to the
terminals labeled “A” and “B”.

TWO WIRE INTERFACE

In general, the advantage to the Two Wire Interface is
the inherent higher noise immunity, especially when
connected over long distances. It also offers a
simpler interconnect with fewer wires. In the Two
Wire Interface the signal conditioner is connected to
the regulated power supply through a series dropping
resistor. The pulsing action of the signal conditioner
causes a modulating current flow through the series
resistor, producing a near symmetrical square wave
signal output.

Figure 2 illustrates the typical output signal produced
by the two wire interface. Note that the minimum
excursion of the output signal does not return to a
zero volt or ground reference. This characteristic of
the two wire interface may cause some difficulty in
selection of the frequency counter or rate indicator. A
typical “TTL” compatible interface requires that the
minimum signal excursion be near zero volts. Some
indicators may require the signal to pass through
zero, going negative. A level shifting device or DC
blocking capacitor may be required to remove the
unwanted DC component. If these are not possible
alternatives, the Three Wire Interface should be
considered.

Figure 1A. Typical hook-up for a Two Wire Interface. Connect
flowmeter pick-off terminals “A” and “B”. Jumper terminals “O” and

“C” as indicated. Select R
instructions.

and supply voltage according to

series

Figure 1B. Typical Three Wire Interface. Connect flowmeter pick­off at terminals “A” and “B” as shown. No connection to terminal

“O”. Pull-up resistor R

selected according to instructions.

p

Model 106-255 Signal Conditioner, Modulated Carrier, Meter Mounted

p

pply

Selection of the power supply level and series resistor
value in Figure 1A is not critical, however, certain
guidelines should be followed. The signal conditioner
is designed to operate at supply voltages between 15
and 28 volts DC. The maximum current drawn by the
signal conditioner is determined by the selection of
power supply voltage and resistor. A supply with a
minimum output current capability of 100 milli­amperes should be provided to assure stable signal
output. The resistor value selected should not be so
large as to limit operating current to the signal
conditioner. Figure 3 graphs the maximum resistor
vs. supply voltage. In using this graph, select the
minimum expected value of supply voltage and read
the corresponding maximum value that may be
selected for the series resistor. For example, if the
minimum expected supply output is 22 volts, the
maximum valued resistor that should be used is
approximately 330 ohms. For most installations, a 1
watt carbon composition resistor will be adequate.

Figure 4 gives the output peak to peak voltage vs. the
series resistor value for a range of power supply
voltages. The shaded area to the left exceeds the
maximum resistor selection and is excluded from the
useable range. Figure 5 provides the minimum value
signal excursion or DC component. Peak to peak and
minimum signal are illustrated in Figure 2.

Figure 2. Typical output signal for the Two Wire Connection.

is a positive level on which the signal rides. V

V

min

eak to peak swing of the output signal.

p-p

is the

The jumper indicated between terminals “O” and “C”
is required for proper output. This connection enables
the internal switching transistor which produces the
modulation of the supply current.

THREE WIRE INTERFACE

The Three Wire Interface illustrated in Figure 1B
provides an output signal which can be directly
connected to counters or indicators defined as being
TTL compatible. Unlike the signal output from the
Two Wire Interface, the signal output from this
configuration will provide a near zero minimum signal
excursion. The maximum or peak output signal is
determined by the user. An additional wire is required
and, depending on the requirements of the external
system, a second power supply level may be needed.

As in the two wire interface, the flowmeter pick-off is
connected directly to terminals “A” and “B”. The
power supply required can be at any voltage level
between 15 and 28 volts and should be capable of
supplying a minimum 100 milli-amperes. This is
connected directly to terminals “+” and “-“ as
illustrated.

No connection is made to terminal “O”. Terminal
“C” provides the output signal to the frequency
counter or rate indicator. As this output is from an
“open collector” source, a pull-up resistor Rp is
required. The pull-up resistor must be connected to a
positive supply level generally equal to the maximum
desired signal excursion. If interfacing directly to logic

Figure 3. Maximum value for R
su

voltage.

in ohms vs. power

series

2