Flow transducer interfacing?
 

I have gotten an extraudinary deal on a really nice flow transducer that
will make a great remote product readout for my watermaker. The problem is
that it has sinking and sourcing outputs. I want to use it for input to an
LM2907 frequency to voltage converter but the LM2907 requires a crossing
voltage from positive to negative for the pulses. How do you turn a
positive to zero pulse into a positive to negative pulse when you only have
12V+ to work with?

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

"Glenn Ashmore" wrote in message
news:SuTJd.23349$EG1.9142@lakeread04...
I have gotten an extraudinary deal on a really nice flow transducer that
will make a great remote product readout for my watermaker. The problem
is
that it has sinking and sourcing outputs. I want to use it for input to
an
LM2907 frequency to voltage converter but the LM2907 requires a crossing
voltage from positive to negative for the pulses. How do you turn a
positive to zero pulse into a positive to negative pulse when you only
have
12V+ to work with?

That depends on which LM2907 you have: the 8 pin version has one input of
the comparator grounded so the other needs a read AC voltage. Here you can
connect a resistor of 100k from input to ground and couple the output of the
flow transducer to the input with a capacitor of 10uF. This may be an
electrolythic type, with the plus to the transducer and the minus to the
LM2907 input/resistor. This will create a true AC voltage on the input of
the LM2907.

If you have the 14 pin version of the LM2907, you can put the inverting
input at half VCC with a voltage divider: two resistors of 10k in series
between 12V and ground and the "middle" connected to the inverting input of
the LM2907. Bypass the this input to ground with a 10uF elco. The sensor
output can then be connected directly to the non-inverting input op the
LM2907.

Regards,
Meindert

Bingo! That was simple. 112 pulses = .5 GPM= 5V. Think I will go to an
LM2917 for the final version though. I calibrated it for 13.8V and the
output varries about .15V when I increase the supply voltage to charging
levels. The built in zener should eliminate that problem.

Now to find the instructions for this cheepo digital panel meter to figure
out how to move the decimal point.

Anyone have a need for an inexpensive digital flow readout? The eBay
auction was for a lot of five. They are Gem RO paddle type flow transducers
that can be set up for .1 to 1.0 GPM or 1 to 10 GPM.

OTOH, now that I am on a roll I may build digital counter for an excessive
showering alarm in the crew's head. :-)

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

"Meindert Sprang" wrote in message
...
"Glenn Ashmore" wrote in message
news:SuTJd.23349$EG1.9142@lakeread04...
I have gotten an extraudinary deal on a really nice flow transducer that
will make a great remote product readout for my watermaker. The problem
is
that it has sinking and sourcing outputs. I want to use it for input to
an
LM2907 frequency to voltage converter but the LM2907 requires a crossing
voltage from positive to negative for the pulses. How do you turn a
positive to zero pulse into a positive to negative pulse when you only
have
12V+ to work with?

That depends on which LM2907 you have: the 8 pin version has one input of
the comparator grounded so the other needs a read AC voltage. Here you can
connect a resistor of 100k from input to ground and couple the output of
the
flow transducer to the input with a capacitor of 10uF. This may be an
electrolythic type, with the plus to the transducer and the minus to the
LM2907 input/resistor. This will create a true AC voltage on the input of
the LM2907.

If you have the 14 pin version of the LM2907, you can put the inverting
input at half VCC with a voltage divider: two resistors of 10k in series
between 12V and ground and the "middle" connected to the inverting input
of
the LM2907. Bypass the this input to ground with a 10uF elco. The sensor
output can then be connected directly to the non-inverting input op the
LM2907.

Regards,
Meindert

Glenn Ashmore wrote:
snip
OTOH, now that I am on a roll I may build digital counter for an excessive
showering alarm in the crew's head. :-)

Alarm? You're too soft hearted Glen! You need something more creative.
Like a counter that shuts off the warm water or maybe even cuts in the
chill water from the ice maker. :)

Jack

--
Jack Erbes in Ellsworth, Maine, USA - jackerbes at adelphia dot net
(also receiving email at jacker at midmaine.com)

"Jack Erbes" wrote

Alarm? You're too soft hearted Glen! You need something more creative.
Like a counter that shuts off the warm water or maybe even cuts in the
chill water from the ice maker. :)

I would but I can't find a good price for 12V solenoids on eBay. :-)

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com