chocolate tank level control advise
chocolate tank level control advise
(OP)
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
thanks in advance for any help





RE: chocolate tank level control advise
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.
RE: chocolate tank level control advise
xnuke
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RE: chocolate tank level control advise
Can't you try a load cell to measure the weight of the whole tank and chocolate together?
RE: chocolate tank level control advise
load cells are the usual method of choice, rememeber you'll have to class A the tank from time to time...
RE: chocolate tank level control advise
RE: chocolate tank level control advise
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
RE: chocolate tank level control advise
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
RE: chocolate tank level control advise
Cheers
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RE: chocolate tank level control advise
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.
RE: chocolate tank level control advise
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
RE: chocolate tank level control advise
Kind Regards..... Chris.
RE: chocolate tank level control advise
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
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RE: chocolate tank level control advise
RE: chocolate tank level control advise
Regards,
RE: chocolate tank level control advise
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
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RE: chocolate tank level control advise
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.
RE: chocolate tank level control advise
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
RE: chocolate tank level control advise