Static Pressure Transducer

[duke of earl]

Hello Gents,

I have a Trane PCM that I am trying to marry a Veris Industries PX Series transducer to. The PCM AI is Configured for 0-10vdc and the sensor selected in the software setup is a "supply duct static sensor 5" wc".There is about .8 inches difference in the readings between the transducer display and the pcm.Anyone know what the range and offset should be for this transducer? None of the sensors that I select in the pcm ai setup seem to match.

[controldude]

Set the transducer for 0-10vdc, unidirectional, response time 2seconds then
set range=5, offset=0 this according to the veris worksheet stating 0-10 vs. 2-10vdc and my range and offset calculator

[crab master]

http://veris.com/product.asp?idMainCategory=46&idCategory=171&idProduct=57

The above link is the new model

I have attached the older model data sheet as well.

First thing I would check is the range that is set in the Veris transducer itself. Make sure it is set to 5" w.c. With that said I am not familiar with your software but are you sure your software isn't filtering the incoming value on the transducer to slow down the reading and if you just wait for your pressure to stabilize your reading may as well? Also are you really running near 5" w.c? Most of my applications I am running around 1.5" w.c so I set my transducers for 2.5" to have a more valid range to get the best possible reading and of course I set my software point up as well to have a range of 0-2.5"wc so all matches.

I would also get a volt meter on the pressure transducer input and see if you are getting a voltage drop due to wire length/under sized. You can do the math for the transducer at 0" you should have 0 volts, at 2.5" you should have 5 volts and 3.75" you should have 7.5 volts, and at 5" you should have 10 volts. Hopefully the transducer has a LCD and you can just have someone look at the LCD display and tell you what the reading is while you are checking it.

[duke of earl]

Thanks guys. I actually tried 0 for offset and 5 for range and it worked perfectly. I stumbled onto these numbers when the old transducer setup was set at 6.2 and -1.2. With the fan off the static reading was -1.2.The lightbulb went of and I went with what felt right and used 0 and 5. Perfect combination.BTW what does Bidirectional mean?Unidirectional?

[crab master]

Bi-directional will read positive and negative values.
Uni-directional basically will only read positive or negative values, not both.

[duke of earl]

Well I am digging up bones here because I am having a problem with this setup all of a sudden. After a couple of months of operation, all of a sudden when this air handler goes into occupied mode the fan does not ramp up.My PCM is enabling the start/stop BO to the VFD(Toshiba E-3) but the analog signal remains at -10.0. With the fan off and duct static at 0" the AI shows failure at end of range. I think this failure is keeping PCM from running the fan. I have a PCL routine for fanfail and I disabled it temporarily to see what would happen. No change unfortunately so I re-enabled the routine. If I go into manual mode and give a signal the drive ramps upto the signal speed. Then I exit manual mode and the drive stays online and is controlled by PCM.Maybe there is another way to configure this AI for duct pressure. It is set for "LIN", Range-5, Offset-0. Any way around the fail at end of range on this?

[qtip]

Sounds like the fan in not proving "on" at minimum speed when the fan starts. Check fan switch or adjust min speed of the drive.
Typically after the fan starts there needs to be a proof of operation before the PID will control the fan speed.

[duke of earl]

qtip,

Actually, the fan never begins to ramp at all to give the air proving a chance.I thought about it some today and thought about setting the transducer to bi-directional and using -3" at0vdc and +3" at 10vdc for the pcm to use. This way the "Fail at end of range" would be -3" instead of 0". Now a new problem arises where if the transducer does fail but the PCM does not acknowledge the failure, if the pcm sees low static it will ramp the vfd to 60hz and kaboom-blow the duct apart. Any other ideas?

[mikesands]

Static pressure safety switch, a transmitter doesn't replace a safety switch. There is no need to read a negative pressure on a supply fan, you're junking things up. Just use unidirectional. If you are getting errant voltage readings out of the Veris transmitter install 2.2K ohm resistor across its output.

[crab master]

Static pressure safety switch, a transmitter doesn't replace a safety switch. There is no need to read a negative pressure on a supply fan, you're junking things up. Just use unidirectional.

Agreed - you need to install a high static pressure safety that is manual reset and shuts down the fan no matter what if it trips, as in even if the VFD is in manual mode. It should be sensing somewhere between the outlet side of the fan and any fire dampers. Make sure you don't install the sensing location downstream of any dampers!

Is your analog signal really -10 VDC or are your leads just reversed?

With this all of the sudden I am wondering if someone changed some parameters in the VFD or if some fingers have changed some wiring or other parameters? I don't recall working with Toshiba VFDs or the type of setup that you have.

[short243]

Well I am digging up bones here because I am having a problem with this setup all of a sudden. After a couple of months of operation, all of a sudden when this air handler goes into occupied mode the fan does not ramp up.My PCM is enabling the start/stop BO to the VFD(Toshiba E-3) but the analog signal remains at -10.0. With the fan off and duct static at 0" the AI shows failure at end of range. I think this failure is keeping PCM from running the fan. I have a PCL routine for fanfail and I disabled it temporarily to see what would happen. No change unfortunately so I re-enabled the routine. If I go into manual mode and give a signal the drive ramps upto the signal speed. Then I exit manual mode and the drive stays online and is controlled by PCM.Maybe there is another way to configure this AI for duct pressure. It is set for "LIN", Range-5, Offset-0. Any way around the fail at end of range on this?

Ok, I'm confused, the BO is enabled, fan is off .... fan should start and go to min Hz, after proving fan on, PCM will then ramp up drive. What is your end of range set at, I ask the question to able to understand your settings.
I am curious as to why the fan stays on AFTER the fan is running but does not start and go to min Hz at command from BO, and why it will ramp when you manually give it a signal. I think I would first look at the settings in the drive. Maybe fingers has payed you a visit .......