Applications

12 Channel NEMA 4 Temperature Recorder

The Maintenance Mgr. of a steel plant in the Midwest called with an application for a portable recorder that can measure, record, save and print temperatures of 12 zones in a high temperature oven. We knew we could do it because we recently put together a similar portable recorder for an asphalt plant here in Pennsylvania. That customer wanted a recorder with both type K and type J thermocouple inputs with a strip jack panel for quick disconnect in the field. They use it to provide asphalt production temperature documentation to the state of Pennsylvania when doing a state funded project.

 

Manufactured for a Steel Plant

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Manufactured for An Asphalt Plant

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One of the challenges was to find a suitable enclosure to house the recorder. Recorders are typically long and narrow. A recorder 6″ x 6″ x 10″ long would require a very large enclosure due to the 10″ depth. Deeper panels generally have a large front panel. Fortunately, we have access to a custom panel manufacturer that supplies us with handmade fiberglass and metal enclosures fabricated to fit the instrument perfectly – and no larger. We even specify front and back hinged doors which facilitates access to the chart and pen up front as well as downloading data to a memory stick. The customer can also easily access wiring through the back door. And of course a nice ergonomic handle for toting it around.

It turned out beautifully. Another satisfied customer. Have a look for yourself –

Tech Tips

How to Check a Thermocouple (Part 2)

Part 2 of a 2 part series with Wayne Cooke Sr.

C. Check for proper polarity. Many thermocouples are terminated with connectors or a transition where it is possible to have a reverse connection. That is, the negative wire is connected to the positive pin of the connector and positive wire is connected to the negative pin. When heat is applied to the thermocouple with the sensor plugged into a temperature tester, the reading will go down as the temperature goes up.

blogNote: It is not unusual to also see what is known as a “double reverse” connection. Here is an example. Customer has a type K thermocouple terminated with a screw cover head on top of a hot furnace. The electrician connects the wire in the head in reverse. Negative to positive and vice versa. He walks back to the controller 50 ft away and observes that the temperature is reading in the negative direction. Obviously he has a reverse connection. Instead of getting the ladder back out and climbing up on top of the hot furnace, he reverses the connection at the terminals of the controller and sure enough the controller reads in the positive direction. Problem solved? No. He must go back and correct the wiring because he still has the chromel wire connected to the alumel and vice versa in the run of wire from on top of the furnace (where the ambient temp in the screw cover head might be 150 F) and the terminals on back of the controller (where the ambient temp might be 70 F). The result is the same as it would be if he used uncompensated copper wire between the 2 connections and the reading will be off by 80 F (150-70 = 80). Remember red is always negative when working with a thermocouple and usually positive in a standard electrical connection so it is easy to get that mixed up.

D. If you want to determine if your thermocouple or the instrument it is connected to is bad, try the following. Disconnect the thermocouple from the temperature controller or PLC input module and short across the 2 input terminals at the controller. If the controller reads ambient at the terminals, the thermocouple is most likely the problem. This is not always true for all controllers as I’ve seen a few where you must connect a thermocouple to the instrument terminals so it is best to take a short piece of thermocouple wire, strip both ends and twist securely at one end to form a junction and connect the other end to the input terminals and see if you read ambient temperature.

Tech Tips

How to Check a Thermocouple (Part 1)

Part 1 of a 2 part series with Wayne Cooke Sr.

A. Check for continuity by using a multimeter set up to measure ohms. Connect the multimeter test leads to the 2 thermocouple leads (polarity doesn’t matter for this test) and if the meter reads 0 or open circuit, then at least one of the thermocouple leads are broken. Could be at the tip and not visible to you or could be somewhere along the lead wire portion of the assembly.

blogIf you do get a reading it should be several ohms (for a short assembly) to 20, 30, 50 ohms or more depending on the lead length. Ex: a 4 ft. length of 20 gauge type J (iron-constantan) lead wire = 1.396 ohms (.349 / ohm per combined ft. x 4)

B. To determine if a thermocouple is grounded or ungrounded, perform this check. Using the multimeter in the resistance measuring mode, connect one lead of the meter to one lead of the thermocouple and touch the other meter lead to the sheath of the thermocouple. The meter should read 0 or open if that lead (or side) of the thermocouple is ungrounded. Repeat test on other lead of thermocouple and observe reading. If open that lead is also isolated from the sheath and the sensor is ungrounded. Grounded thermocouples are more responsive to a change in temperature while ungrounded thermocouples are useful when there is electrical noise in the area of the thermocouple and that noise could be induced into the sensor.

Note: When checking an “ungrounded” thermocouple, it is possible to have some leakage to ground in a mineral insulated thermocouple. It is difficult to keep the magnesium oxide insulation in a mineral insulated thermocouples (MgOs) completely dry. Most of the time this is not a problem when it’s connected to an instrument or PLC input module, even though you might see some resistance to ground in the megaohm or even kilohm range. When the thermocouple is heated in the process, it tends to drive the moisture out of the tube and create better isolation.

Uncategorized

Charlie’s Smokehouse

In 2009 we received a call from a fellow who identified himself as “Charlie of Charlie’s smokehouse in Wisconsin”. Naturally, the first thing that came to mind was meat! It turns out that Charlie is the proprietor of “Charlie’s Smokehouse” located in Ellison Bay, Wisconsin on Lake Michigan and they smoke fish – not sausage – freshly caught from the deep blue waters of the Lake.

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Charlie, like many owners of food processing plants, is paid a visit periodically by the FDA – in Charlie’s case, the food safety division of the Wisconsin Department of Agriculture. The Department inspects the facility and verifies that the company has their HAACP program in place and working. HAACP is an acronym for Hazard Analysis & Critical Control Points and is a management system in which food safety is addressed through the analysis and control of biological, chemical, and physical hazards from raw material production, procurement and handling, to manufacturing, distribution and consumption of the finished product. For more information on HAACP visit http://haccpalliance.org/alliance/haccpqa.html.

 

Years ago, the manufacturer or processor would check the temperature in the smoke house and the cold storage facility with a bimetal thermometer and write the readings down on a piece of paper. Then along came circular or strip chart recorders. Recorders require some maintenance, including changing charts and pens daily or weekly. When Charlie called he was looking for a more “modern day” solution so we recommended the Madgetech Quadtemp2000 – a multi channel datalogger – which accepts up to four thermocouples simultaneously, records temperatures for weeks at a time and can be downloaded to a computer and displayed in an excel spreadsheet or emailed to the appropriate government agency, customer, etc. Within days Charlie had his new automated HAACP compatible temperature logging system up and running.

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No more daily trips to the smokehouse and cooler to manually record the temperatures or fiddling with charts – it’s still running perfectly today. I know because I recently spoke with Charlie to order my smoked fish for the holidays. It is really tasty and I highly recommend it. I save some to make fish dip. Yum! Go to Charlie’s website and see for yourself!

Applications

Fishing With Thermocouples

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At W. H. Cooke & Co., we get phone calls in regards to thermocouple applications from engineers, purchasing agents, maintenance folks, and in this particular case, a fisherman named Frank. This gentleman is a fisherman in the Great Lakes region and he told me that he has found that the fish like to swim below the surface of the water in a specific temperature range.

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He was looking for a way to detect the temperature of the water where his hook will be. We designed a thermocouple for him that he could attach to his line, just above the hook. We used a 1/2” x 1/2” stainless steel hex nipple fitting to act as a sinker with a small probe exiting the front of the bore of the nipple. Water resistant epoxy was used to seal the front of the nipple as well as the back of the nipple where the waterproof Teflon leads exited. Back on the boat, we sold Frank an Extech TM100 that he could use to read the thermocouple.

TM100

 
Now, he lets out enough line from his rod until he hits the depth where he knows the fish are biting and reels them in. Frank is a 21st century fisherman and while we don’t expect that everyone is ready to attach a thermocouple to their line and cast out, perhaps we can help you with a different unique application. You dream it, we’ll make it.

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