rpoet
Member
Hi All,
I don't do much analog, and I do even less with 4-20ma current loops. Here's what I'm thinking of doing; I'd like a double check so I don't do something silly.
I'm using these transducers to sense the height of a 48" water column in two seperate water tanks. I'll place it at the output of each water tank I'm sensing, which is at the bottom.
The important specs are:
0-5 PSIG
4-20ma output
http://www.dwyer-inst.com/Products/Product.cfm?Group_ID=98&sPageName=ModelChart#specs
I plan to use this panel meter:
http://www.lascarelectronics.com/temperaturedatalogger.php?datalogger=390
It can accept and display two separate voltage inputs with ranges to 0-40vdc (zero and span are adjustable in software).
I plan to convert my 4-20ma signals to voltage inputs at the meter with precision 500 ohm resistors across the input, to ground.
http://www.mouser.com/ProductDetail/Vishay/CPF1500R00FKE14/?qs=TaOZSEYtRiU3zlX9L2fWjg%3d%3d
Sensors will be tied to the meter with Belden 8760 cable; it's 18-2 twisted pair with a drain wire. One-way distance for the cable runs will be approximately 150'; 300' loop.
I plan to feed the whole thing with a 24vdc power supply. According to the data sheet, the meter seems to be OK with it's power supply sharing a ground with the analog inputs. I realize that I will have a live zero and that's fine, as I can account for that in the meter's setup.
Since the meter's zero is adjustable, I will empirically determine what my setting for "empty tank" will be by measuring the voltage across the resistor with the tanks empty.
Likewise, I'll determine what my setting for "full tank" will be by simply filling the tanks with water and measuring the voltage across the resistors. This should give me my span so the meter displays "full" when the tanks are full.
The relationship between water column height and tank fill should be directly proportional, as the tanks I'm sensing are simple cylinders.
Anyone see any pitfalls with this setup? Thanks for the help!
-rpoet
I don't do much analog, and I do even less with 4-20ma current loops. Here's what I'm thinking of doing; I'd like a double check so I don't do something silly.
I'm using these transducers to sense the height of a 48" water column in two seperate water tanks. I'll place it at the output of each water tank I'm sensing, which is at the bottom.
The important specs are:
0-5 PSIG
4-20ma output
http://www.dwyer-inst.com/Products/Product.cfm?Group_ID=98&sPageName=ModelChart#specs
I plan to use this panel meter:
http://www.lascarelectronics.com/temperaturedatalogger.php?datalogger=390
It can accept and display two separate voltage inputs with ranges to 0-40vdc (zero and span are adjustable in software).
I plan to convert my 4-20ma signals to voltage inputs at the meter with precision 500 ohm resistors across the input, to ground.
http://www.mouser.com/ProductDetail/Vishay/CPF1500R00FKE14/?qs=TaOZSEYtRiU3zlX9L2fWjg%3d%3d
Sensors will be tied to the meter with Belden 8760 cable; it's 18-2 twisted pair with a drain wire. One-way distance for the cable runs will be approximately 150'; 300' loop.
I plan to feed the whole thing with a 24vdc power supply. According to the data sheet, the meter seems to be OK with it's power supply sharing a ground with the analog inputs. I realize that I will have a live zero and that's fine, as I can account for that in the meter's setup.
Since the meter's zero is adjustable, I will empirically determine what my setting for "empty tank" will be by measuring the voltage across the resistor with the tanks empty.
Likewise, I'll determine what my setting for "full tank" will be by simply filling the tanks with water and measuring the voltage across the resistors. This should give me my span so the meter displays "full" when the tanks are full.
The relationship between water column height and tank fill should be directly proportional, as the tanks I'm sensing are simple cylinders.
Anyone see any pitfalls with this setup? Thanks for the help!
-rpoet
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