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kromann (Mechanical) (OP)
12 Sep 03 10:27
I am trying to find a level sensor/method for a chocolate day tank to control the automatic replenishing of it as the chocolate is consumed by the process. The control does not have to be precise, the level could vary over possibly 12" and not affect the process. The fill valve that will be used will be just on/off. At the bare minimum I need to know when the level drops below a certain height, but having the ability to know if their is an overfill or empty situation would be handy to allow an alert to be sent. The cylindrical, angled bottom day tank (100 gallons) will have an anchor style scraped agitator in it, so inserting into the side at different levels doesn't sound like an option. The vibrating tuning fork method has been suggested to me, but that will only indicate if the level drops below a certain level. I am also concerned about that sensor's behavior when chocolate adheres to it and then hardens. Any advise would be helpfull. After reviewing some of the other posts I'm leaning towards one of the radar methods.

thanks in advance for any help
Helpful Member!  ab123456 (Chemical)
12 Sep 03 10:52
I have no experience with chocolate but do have experience with both radar and tuning forks on dirty products.

We have found radars to be very reliable, the only thing I would say about radars is to pay attention to manufacturers recomendations about where on the tank you locate the radars to avoid multiple echos. Have you considered ultrasonics? they are cheaper than radar although we never got them to work reliably and therefore settled on radar.

We also use tuning forks as a hardwired high high level device on these tanks, however whenever they are triggered we have to remove them from the tank to clean them.
Helpful Member!  xnuke (Electrical)
12 Sep 03 11:24
I've used ultrasonic sensors successfully. Just prevent it from being coated with chocolate.

xnuke

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

Helpful Member!  zimbali (Automotive)
12 Sep 03 14:24

Can't you try a load cell to measure the weight of the whole tank and chocolate together?

Helpful Member!  hacksaw (Mechanical)
12 Sep 03 16:55


load cells are the usual method of choice, rememeber you'll have to class A the tank from time to time...
tiffy023 (Industrial)
16 Sep 03 11:13
I've used radar types successfully for this sort of application before and you can actually set up the instrument with the agitator running and enable the instrument to 'ignore' the agitator movement (if this is required). Hope this helps
Helpful Member!  brianslater (Industrial)
18 Sep 03 15:23
Hi Guys
I agree with the radar approach as being the most reliable, but its expensive and maybe an overkill for a daytank on off level.
I presume there is some heating jacket to keep the chocolate above 80C?
You might consider a set of vertical capacitance probes top entry from the tank roof. these are ptfe coated and may resist coating, if you have a reasonable temperature inside the tank? Certainly a lot cheaper than radar and widely used in the water industry.
Ultrasonics are hit and miss and cheapest, might work for you or not, only thing is to suck it and see (no offence to choclatiers). You must keep the head from getting coated with chocolate mist - I presume you get some kind of condensation on the tank roof?
Load cells are also of good method, but expensive, and they dont like welders
kromann (Mechanical) (OP)
19 Sep 03 10:03
Thanks everyone,
load cells were considered, but too late to incorporate into the mounting easily. Additionally, it appeared we would have to run a flex line from the discharge of the tank to the pump instead of a jacketed one to use them, which brought up the issue of gradual build up in the line. With the viscosity of chocolate being so high, I was trying to get the pump as close to the discharge of the tank as possible.The tank is jacketed, water between 40 and 47 C depending on status of system. The chocolate definatly coats anything it touches and then quickly sets up unless heated, so vertical capacitance probes, even teflon coated, didn't appear to be a solution unless they could be heated and maybe vibrated. I'm leaning towards radar at the moment, since what I am picking up on is that ultrasonics work sometimes , but there would be a good chance I would have to go to radar if the ultrasonics didn't cut it.
thanks again,
kromann

zimbali (Automotive)
19 Sep 03 18:10
I wish ultrasonic works, they are actually good especially in a case like yours. There is no reson it won't work (theoritically!). Let us know if it works properly and good luck.


Cheers


You can live in your car, but you can't drive your House!

navvin (Electrical)
24 Sep 03 5:44
I'm in petrochem, so not very familiar with Chocolates (except that I eat, lavishly!).

Radars should be the right solution, since we use the same technology for Liquid Sulfur levels as well. Guided Wave Radars (Magnetrol / Emerson) would have been a cheaper solution, but then you need to keep the chocolate away from coating (with heating coils inside the tank). Emerson has a wide variety of Radar Level instruments in their product range, including SAAB radars (non contacting, very accurate but highly expensive, mainly used for custody transfer appn.), so better to check with them for proper & commercially viable model. You may check with Enraaf as well since they must be cheaper to Emerson.
jhadk (Electrical)
1 Oct 03 5:56
on harsh and sticky things use weigh systems .
other option to weighing is radar level tx. if environment is clean,ie no fumes,no steam etc over the surface, ultrasonic level is another solution.
for perfect solution, send complete process and equipment details. rps saini.ips automation products p ltd .at ips@glide.net.in.
regards
Kirst (Bioengineer)
22 May 04 14:20
I suggest you to use ultrasonics rather than radar or load cells. Radar are a very precise devices and are very expensive because of that. You said you donĀ“t need it to be very much accurate. Load cells are good but the work for installation and tuning a load cell in a tank very big is also very big. So that's why arecomend you to use a Ultrasonic sense, it is cheaper, easy to install and provides a continual signal that you can use in the way you prefer. We use it in our plant with very good results. JUST FORGET VIRATIONAL FORKS SENSOR!!!!!!! They're not good for our type of fluid.

Kind Regards..... Chris.
jmw (Industrial)
22 May 04 19:29
Not all Radar systems work the same, deliver the same performance or cost the same.
I believe the Solartron Mobrey radar level system is about half the cost of, say, a Saab. Not as accurate but you indicated that wasn't a problem.
Take a look at www.solartronmobrey.com and compare with the other radar systms out there.

JMW
www.viscoanalyser.com
Eng-Tips: Pro bono publico, by engineers, for engineers.

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

lexonrey (Materials)
24 May 04 10:27
     Viscosity of liquid pitch must be similar to hot chocolates. And the only level sensor that worked for us, on 60 meter high storage tanks, is Radar. We tried everything that was mentioned , only radar worked to this day, and we are talking about liquid pitch storage tanks that is heated, average 50 to 60 degress centigrade, recirculated through heaters all the time. It is expensive though.
quark (Mechanical)
28 May 04 5:32
I don't think you will have problems with vibratory tuning fork level switches. You require two switches,one for low level and one for high level. When you require only two point control, I don't suggest to go for rather expensive devices. Though the chocolate sticks to the tuning forks,when the vessel is empty the resistance to the fork movement decreases and this can be well detected.

Regards,

jmw (Industrial)
28 May 04 6:51
I appreciate that while Kromann refers to a level senor, his application quite reasonably can be solved with high/low level switch control, if it can be realised economically. There is an attraction to fork vibrational level switches, mainly they are cheap and usually maintenance free.

However, I would be unhappy with a tuning fork sensor, (or any other invasive device) in this application without a proven history of success.

Sure, a clean sensor at the high level will show it is in air.

When the chocolate first reaches it, it will show the chocolate.

As the level falls, the fork may then be left coated. This may leave the device in a false high state or an alarm state.

If the fork is coated but otherwise exposed to air (or deprived of direct heating from the chocolate it was immersed in) the chocolate may set. This may cause the sensor to lose lock, i.e. the drive circuit cannot find resonance.

Insertion through the side of a jacketed tank would be a major undertaking and costly if appropriate insertion points do not already exist. The heating from the jacket may prove sufficient to help keep the sensor functional but I would be suspicious of this.

If the tank is not jacketed then the heat loss effects, especially as the sensor may act as a heat sink, will be noticable.

The option for jacketed tanks would be for top mounted fork (or ultrasonic) sensors on long stems.

When the chocolate level rises again the surrounding chocolate may thaw out the chocolate coating and allow the switch to reset and resume function. However the chocolate level may have risen significantly above the switch by this time.

In the case long stem top mounted fork sensor(s) the sensors will now be out of contact with any direct heating. In fact conduction losses may even affect the immersed (low)sensor, sufficient for the chocolate in contact with it to set, despite any surrounding fluid chocolate, with the possibility of false alarms.

Also, dependent on how high up the stem above the fork the chocolate reached, the time the fork remains coated with fluid chocolate will depend on the drain time of the chocolate from the stem. More sustained false high signal and greater potential for some chocolate to solidify.

This same effect could cause the low sensor to remain in a high alarm condition even when the tank is otherwise drained (meaning the tank could empty, starving production).

One cannot assume the device will be sophisticated enough to remain functional.
Most fork level sensors have a fairly basic drive circuit. They are dependent on detecting a significant difference between resonant frequency from one state to the next. A tuning fork level switch costing $100 is not as sophisticated as a tuning fork density meter at $2-3000 and it would also be expected to have problems.

Float switches, tuning fork level switches or whatever intrusive device is considered, great care should be taken to discover if the device has a history of success in this application and under what circumstances.

Sometimes the lower cost of the device is negated by the added cost of the work-arounds. For example, in some applications where coating can occur, it is neceesary to include a spray nozzle just to clean the device, or a sensor heater. When this is the only sollution, it is a good sollution. When other technologies will do the job better, it is not.

The idea of a non-ivasive device is far to be prefered. One of the strengths of non-contact devices is in just such applications as these.  The device may cost more to buy but pay for itself in no time at all. In this case while the application allows for high/low switches, a top mounted level measurement system such as radar, optical or ultrasonic may be preffered.

JMW
www.viscoanalyser.com
Eng-Tips: Pro bono publico, by engineers, for engineers.

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

Helpful Member!  FrancisL (Computer)
29 May 04 17:41
Measure or estimate the inflow and outflow and integrate to get the level.
When you really have emptied the chocolate tank (after CIP?) reset the level estimate to zero.
You only need to know the inflow and outflow, and even without flow transmitters you may be able to put an estimate into a simple equation.
Get someone to do a visual check from time to time and provide a user interface for them to enter a new estimted level.
nbucska (Electrical)
3 Jun 04 20:27
Use a float, mounted on a rotating arm. On the float
mount a permanent magnet. Sense the magnet's position
with one or more read switches.

You can have millimeters of tolerances.
It will work until/while/when the chox is molten.  

<nbucska@pcperipherals DOT com> subj: eng-tips

PigskinPapa (Electrical)
22 Aug 05 15:56
RF Admittance is the only way to go in this case.  It won't be affected by crusty buildup.  

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