Level sensor and pressure meter application, please advise if you have experience.

[flyers]

Hi guys,

Appreciate it if someone has experience in these application can give me some feedback.

For application A, the 1200 liter Tank containing IPA solution, I want to get a device which can give me level indication (low, high & high high). I do not need to know the volume or exact liquid level, I just need the level indicator back to my PLC to start/stop some pumps & valves. The tank is stainless steel. Please suggest a suitable device to do this.

For application B, the stainless steel panel must be pressurized with N2 gas (one of the customer spec). The panel pressure must be higher than atmosphere so that outside gas will not enter into the panel. Is there a device to measure the N2 pressure which will be mounted outside of the panel? I don't need these signal to PLC, just for the operator to view at the panel itself. Either an analog or digital also can.

Hope to hear from you guys. Thank you.

 

[Ken Moore]

A: Use a standard capacitance type or guided radar level transmitter for low and high, and then add a switch for high-high.

B. Standard pressure transmitter.

There are many vendors for both types of transmitters, Emerson, E&H, Siemens, Foxboro etc...

There are cheaper vendors, but for industrial applications I prefer one of the larger vendors, usually better service, and very dependable.

 

[Norml]

The cheapest level indication would be float switches (Gems, Warrick). You can get them with weights or tie them to a rod which you can lower into the tank. Next cheapest would be a submersible pressure transducer which can put out an analog signal assuming your PLC has analog inputs.
(US Filter makes a nice one). Siemens makes the Hydroranger 200 which is ultrasonic and can put out an analog signal or can be programmed to turn on dry contacts for digital inputs into your PLC. I believe they have 6 programmable relays along with alarm indications such as Loss of Echo.

 

[jbjbj]

flyers,

Your application B implies a hazard duty area.

There very well may be other requirements for the panel to meet local codes.

This may include the use of intrinsically safe barriers, explosion poof or NAMUR type sensors.



In the USA I would use NFPA 496 for a purged and pressurized enclosure.

There are other standards such as ATEX directives.

You should check with the customer which "codes" you need to design to.

Over here, depending on the hazard class rating, it most likely would not be adequate for the operator to verify pressure but the power would also be interlocked with the pressure and a timer that insures that the N2 has been long enough to replace the air inside.

I don't want to overly complicate things but the N2 pressure is a big red flag to me.

 

[Tom Jenkins]

Warick and Omega Engineering and others provide electrode type level switches that look exactly like your sketch. I'm not sure what IPA is, but it must be conductive for these to work.

You may also consider using pressure switches or a pressure transmitter for the level sensing. This is a good technique of the fluid is non-conductive or has a tendency to foul or gum up floats or electrodes.

 

[Norml]

IPA = India Pale Ale

 

[Ken Moore]

IPA = isopropyl alcohol

 

[danw]

>>Is there a device to measure the N2 pressure which will be mounted outside of the panel? I don't need these signal to PLC, just for the operator to view at the panel itself. Either an analog or digital also can.



A differential pressure gauge has two connections. One is plumbed inside the panel, the other is plumbed to outside the panel. The gauge indicates the pressure difference between inside and outside.

They can come with switches or without (just indicating gauges)
http://www.lesman.com/acatalog/Online_Catalog_Differential_Pressure_Gauges_1223.html
Dan

 

[flyers]

Ken Moore, I think for cost saving purpose, a capacitance type level transmitter would be a better choice than the guided rader, tho` i've not come across any guided radar level transmitter, but sounds expensive to me, am I right?

Normi, We taught of float switch also, but the float switch we come across are normally plastic type, in long run, we are affraid there is a chemical reaction between the plastic material and the IPA. Another reason they use s/steel tank and panel for this IPA system because they do not want (or minimize) chemical reaction. I'm sorry, my PLC has no analog input, all are digital only. I think ultrasonic can be another solution, just in case the capacitance/conductive method does not work.

jbjbj, thanks a lot for your concern, i'll look into it, I'm totally new to NFPA & ATEX thingy. I only come across those IP rating/ex rating so far See how fresh I am!

Tom Jenkins, does the electrode type level switches same as Ken Moore's suggestions like the capacitance type? I'll check with the supplier if they know IPA is conductive or not, I myself do not know if they are conductive. FOr the conductive method to work, it's just based on the liquid only or the tank must be conductive as well?

Norml, no idea what is India Pale Ale

danw, is differential pressure gauge same as pressure transmitter, you know sometimes the same thing has many naming. Thanks for your link. I'll check if they have support/sales in my country (Singapore/Malaysia).

 

[danw]

danw, is differential pressure gauge same as pressure transmitter, you know sometimes the same thing has many naming.

An indicator only shows a value. Those devices in the link are indicators or indicator/switches only, not transmitters.

Siemens makes an ultrasonic unit with a dual switch (relay) outputs, where each relay has any deadband/hysteresis setting you want, wide or narrow. So, one could be used for pump-up or pump-down control (where pump-up is turn at low level, stay on until level reaches high level, then turn off), the other switch for a narrow deadband level alarm. It's the model Pointek ULS 200

https://pia.khe.siemens.com/index.asp?Nr=5971

Ultrasonics need about 300mm of blanking zone beneath the bottom of the transducer's diaphragm in which no reading can be made. If the tank needs to be filled close to the top, then an ultrasonic unit needs to be mounted above the tank in some form of stand-off nozzle.

There are relatively inexpensive all stainless steel floats from Gems sensors, for one.

http://www.gemssensors.com/SpecTemplateCustom.asp?nProductGroupID=50

 

[jbjbj]

Level measurements:

The following link to Omega has some nice general info on types of level detecting. ( this link is radiation (radar and such)) Also on the left side bar are links to capactive level measuring. I have never used any devices obtained through these guys but the write ups contain some good general info.

http://www.omega.com/literature/transactions/volume4/T9904-14-RAD.html

 

[Fritz_frederix]

Flyers,

The answer to your question
"is differential pressure gauge same as pressure transmitter, you know sometimes the same thing has many naming"

A pressure transmitter is used in tanks with aan atmosferic outlet. Differential pressure gauges or use when you would like to measure the level of a tank that has N2 blanketing on top. In other words the tank is pressurised with approximetly 100mbar of N2.

Rudi