“Why does NTEP allow the use of non-NTEP load cells for some scales?”

Republished with permission of Jim Truex

National Conference on Weights and Measures

2017 Issue 1
Jim Truex, NTEP Administrator
[email protected]

 

When reading an NTEP Certificate of Conformance (CC) we see the load cell used in a scale is identified as non-NTEP in some case. Many have inquired as to why NTEP allows the use of load cells that are not traceable to their own NTEP CC or “non-NTEP” cells.1

While NIST Handbook 44 does not specifically state that non-NTEP load cells are permitted for use in weighing instruments; Handbook 44 does contain several hints that not all load cells used in commercial scales are required to have an NTEP certificate.

For example:

  • If we look at NIST Handbook 44, Scales Code, Marking Requirements, Table S.6.3.a., the heading of the fourth column reads “Load Cell with CC (11).” This column heading implies that if these marking requirements are for load cells with a Certificate of Conformance, there must be load cells without a Certificate of Conformance or non-NTEP load cells.
  • Also in the Scales Code, paragraph S.6.3., reads in part: “Scales, main elements of scales when not contained in a single enclosure for the entire scale, load cells for which Certificates of Conformance (CC) have been issued under the National Type Evaluation Program (NTEP, and other equipment necessary to a weighing system.” The statement, “load cells for which Certificates of Conformance (CC) have been issued” is also implying there must be load cells without a Certificate of Conformance or non-NTEP load cells.
  • Additionally, if we look at Scales Code paragraph S.5.4. we find the following stated: “This requirement does not apply to complete weighing/load-receiving elements or scales, which satisfy all the following criteria:”
    • the complete weighing/load-receiving element or scale has been evaluated for compliance with T.N.8.1. Temperature under NTEP (meaning the complete weighing device, including load cell(s) has been tested in an environmental chamber);
    • the complete weighing/load-receiving element or scale has received an NTEP Certificate of Conformance;”

Again, no clear statement, but the fact that the formula shown in S.5.4. does not apply if the specified conditions are met tells us that the use of load cells without a Certificate of Conformance or non-NTEP load cells is acceptable when the complete weighing/load-receiving element or complete scale has undergone and satisfied influence factor testing.

So, NIST Handbook 44 tells us that not all load cells have their NTEP certificate but does not tell us why. However, it does tell us that the complete scale (containing the load cell) or weighing element (containing the load cell) must be evaluated for compliance with T.N.8.

To understand more we must go to NCWM Publication 14, Weighing Devices, NTEP Technical Policy, Section B.1., which contains the following statement:

“The main elements and components (indicating elements and load cells) of scales with a capacity greater than 2000 lb. must be tested separately for compliance with the influence factor requirements.”2

Is there any penalty for using non-NTEP cells? Yes, in fact there is a potential penalty for the certificate holder. NCWM Publication 14, Technical Policy allows for the “Substitution of Load Cells in Scales” using a set of specific requirements to determine if the cells are metrologically equivalent. The first requirement in evaluating metrologically equivalent is that both load cells must have been evaluated separately and have a separate load cell Certificate of Conformance. Obviously, since a non-NTEP load cell was used in the cases we are addressing, it does not have an NTEP certificate and cannot be substituted. In these cases, the certificate holder must resubmit the device to NTEP for full performance testing to allow the use of another load cell. Reason being that NTEP does not have values for non-NTEP load cells, such as nmax or vmin to determine equivalency.

Now, we can use this information to piece together the facts pertaining to the use of non-NTEP cells used in complete scales and weighing/load-receiving elements.

  1. NIST Handbook 44 recognizes the use of load cells that do not have their own NTEP Certificate of Conformance.
  2. NCWM Publication 14 recognizes the use of non-NTEP load cells in scales 2000 lb. capacity and less.
  3. The scale or weighing element containing a non-NTEP load cell or load cells must be tested by NTEP for compliance to influence factor (T.N.8) requirements.
  4. If a non-NTEP load cell is used it is identified on the NTEP certificate and the load cell cannot be substituted, otherwise the device must be resubmitted to NTEP for a complete performance test using the different cell. When this scenario happens, an amended certificate identifying the non-NTEP cells used during the evaluations will be issued.

Hopefully this article has helped eliminate some of the confusion and answer questions that may have been on your mind.

 


1. This article was published about two years ago, but we have answered many recent inquiries from the weights and measures community confused about the use the term “non-NTEP” on some NTEP certificates. It appears to be especially confusing when some of the scale models use load cells traceable to NTEP certificate but others, on the same certificate, use non-NTEP certified cells that must be identified on the certificate because of the load cell substitution requirements specified in NCWM Publication 14, Technical Policy. All the scale models listed on an NTEP certificate are covered by the certificate or they would not be listed on the certificate. The “non-NTEP” designation applies to the load cells used in that particular model, version, capacity, etc.

2. Note: If we read further we will find some exceptions but most of those would result in a provisional NTEP certificate not a full NTEP certificate.

Seven Year Support

We pride ourselves in offering our dealers one of the best ranges of weighing instruments available in the North American market. However, we have noticed a disturbing trend where some manufacturers are no longer supporting products with spare parts after only a few years! When spare parts are no longer available, you begin to wonder where your support is. Part of our strategy is to select balances and scales from manufacturers who provide above standard support.

It pleases me to inform you that we at Intelligent Weighing Technology will support all our products for seven years following their sale to you, the dealer. That’s right, seven years. This helps you support your customer by supplying parts and service for a reasonable length of time.

Scales and balances are physical, dynamic, complicated machines. They are not mere “apps” which cost you a monthly or yearly charge until—lo and behold—they tell you that it is no longer supported! These devices are in constant daily use in the real world by real people, and they should be treated and supported as such.

End of rant!

Hello UHR!

Here at Intelligent Weighing Technology we are always looking for ways to improve our product line with newer technology and the features that our dealers and the end users desire in a product. The new UHR Series is no exception. If you have been looking for a replacement for the Sartorius Miras, then you should know that the classic Sartorius Miras bench scale is being phased out in favor of the more dependable UHR bench scale. This newly designed series satisfies a special position in our range: a bench scale that can truly provide 30,000 division performance in terms of repeatability, return to zero and corner loading.

The excellent performance makes this a great product for aerospace, quality control, plastics, research, education and other industrial purposes. The functionality of the indicator is so intuitive that users can be quickly trained in its operation. The huge 2” high Intelligent Backlight™ display clearly indicates the measurements.  A U-shaped bracket on the versatile indicator allows for various viewing angles. The pillar support can also be removed for stand alone use. The indicator may be removed from the pillar and attached elsewhere to accommodate even more viewing angles. And the corrosion resistant cast aluminum bases provide lightness, stiffness and strength.

Configured in three platform sizes; 11” x 13”, 13” x 17.7” and 16.5” x 20.5”, the capacities range from 6 kg to 300 kg. Pounds, kilograms or grams units are available. Not only are the materials chosen to give the best performance, but the load cells are specially chosen for their superior performance. The UHR indicator is quite capable of a stable 150,000 divisions. The animal-weigh filter ensures a stable weight reading. There is a bi-directional RS-232 output for transferring data to printers or computers and the unit will also receive commands from outside devices. The UHR can perform single-weigh with the print button, or accumulation. The UHR is highly serviceable and can be repaired quickly, unlike many bench scales in the market.

Be it in the lab or in the warehouse, the UHR has every benefit of being the most versatile and valuable addition to any industry.

How A Scale Is Protected With and Without a Fuse

Question

An inexpensive scale I bought doesn’t have an external fuse. Should I be concerned?

Answer

As we all know, using electricity carries inherent dangers, so it is important that the electronic equipment we supply is designed to minimize potential hazards. Recent news items about the safety of some of China’s exports illustrate how important this is, and how some unsafe, inexpensive, foreign manufactured products can easily find their way into domestic markets.

You can never assume a product you’re not familiar with is safe; always check a new piece of equipment for proper protective features.  For the end user, unprotected equipment can injure people or destroy property if it develops a fault condition. For the manufacturer and distributor, this can mean liability problems as well as damage to reputation.

The most familiar electrical feature used to protect people and property, the equipment itself, and the power line, is to build a replaceable fuse into the equipment. We all know what a fuse holder looks like, and its presence tells us the device has protection.

With a replaceable fuse, an over current condition like a short, heats the metal link inside which melts. This breaks the flow of electricity; disaster is averted.

But the marketplace always demands more features and benefits for less money. This drives manufacturers to look for ways to lower the cost of what they make and sell, so that black knurled knob on the back of equipment may be the first thing to go. Luckily there are other ways besides a replaceable one-shot fuse to protect a piece of equipment.

One of the interesting aspects of those little black external AC adapters that come with a lot of equipment is that their internal transformer is wound with a smaller diameter wire than a similar transformer built into a piece of equipment. This gives it two advantages.

First, as more current is pulled through the winding, the thinner wire heats up more quickly than thicker wire. As the wire heats up, its resistance also goes up, which limits the flow of current.  So the adapter has a certain amount of inherent current limiting capability.

Second, any wire will melt and open up if enough current is pulled through it. The thin wire of a wall wart is no exception, and it will melt and break, or open, when the current going through it gets above a certain value. We’ve all experienced an adapter that has no output, and what most likely happened is too much juice was pulled through it. The adapter has now become a fuse; a used fuse, at that.

Thin wire in AC adapters is a deliberate design feature to provide current limiting and fusing protections. Personally, I would not rely on these as the sole protection – sometimes a device designed to be “the first thing to go” turns out to be more robust than the sacrificial lamb it is intended to be.

It is also important to realize that a device with an internal battery carries the same hazards and should be properly protected. There is a lot of energy stored inside a battery, and if released all at once (like with a short circuit), a lot of damage can occur.

For equipment with an internal power supply, there are also discrete safety components that can be designed into circuits, the re-settable fuse being a popular one. It is soldered on to the scale’s main circuit board, the same as resistors, capacitors and other components. When the current being pulled through it exceeds a certain point, it opens like a fuse, but will reset itself after the over current condition is cleared.

This component is particularly handy for the end user, as its ability to reset itself when the fault condition is cleared removes the need to keep a supply of various values of replacement fuses handy. Unfortunately these aren’t visible on the outside of the scale, so you have to ask about them, examine the circuit board, or check its schematic to see if one is there.

There are other board level components that can be used, as well.

Unfortunately there are a few foreign manufacturers who just leave all the protection devices out; this is dangerous for everyone.  Very rarely are imports subjected to electrical safety inspections. Make it your duty to find out if the scale has any safety devices built in if none are visible. Uncle Sam is not necessarily going to do it for you. The seller, distributor or manufacturer should be able to tell you what protections are built into the scale. Robust safety protections should give the scale a long, useful, uneventful life; a lack of safety protections should give anyone cause for concern. If you’re not sure, ask!

“Why do I need NTEP?” | National Type Evaluation Program

The National Type Evaluation Program & Why You Need it

Many people ask why they should use an NTEP (Legal for Trade) scale or balance instead of any old scale, surely all scales are the same?

In the USA the NTEP program is recognized by all states, but the interpretation of which applications should use an NTEP scale varies from state to state. There are some state weights and measures agencies, like California, who say that every transaction that uses a weighing machine to determine the price should be NTEP, and some other states do not. Please contact your local Weights and Measures office to see if you need an NTEP scale in your state and which type would be appropriate.

The big question you should ask yourself is not “does the law require an NTEP scale?” but “is buying an NTEP scale the right thing to do for my business”?

NTEP Scale vs Cash RegisterBananas - Food Weight

We all know that starting up a new business or operation takes more time and money than first anticipated, but consider buying a cash register cheaply. It may be made of poor materials, it may be difficult to operate, the drawer may break or there may be many other faults. However, it will very likely always add up correctly even though it makes life a little difficult for you.

Now consider buying a scale or balance cheaply. Whatever you buy or sell is calculated by that piece of equipment. If you sell $300,000 a year of chicken legs and your scale is 1% out (in the customers favor) then you lose $3,000, which is way more than you saved by buying a cheap scale. Consider your scale or balance to be a cash register. It counts your money for you!

Buying an NTEP scale or balance is a protection against poorly manufactured equipment. NTEP scales go through a rigorous set of tests that not only take months, but also cost a great deal. They check to see if the weighing device stays accurate when the temperature changes over time and to ensure the scale will take a lot of abuse, and most importantly that you, the customer, get the correct result.

Recently a customer dealing in precious gems called us and said that he wanted an NTEP scale for the price of the one he had seen that says it is “Accepted in 23 States.” If you see this, this is not NTEP! Those 23 states happen to be those that don’t require NTEP for your purposes. That scale may be legal in those states, but there is no accountability for the supplier to make a reliable product.

If you need legal for trade, always look for the NTEP seal. It may cost a bit more, but when it comes to scales, you get what you pay for!

 

Ask Us | Can I Connect An RS232 Scale or Balance With USB?

Question

My scale (or balance) has a DB9 connector for RS232 serial communications. My old computer had serial ports which could accommodate RS232, but my new computer only has USB ports.  I need to log data from my RS232 enabled scale to my USB enabled computer, what do I do?

AnswerRS-232 female out

Technological progress is usually viewed as a wonderful thing, as demonstrated by the lighting advances in computers. As modern computer
technology marches forward, it would seem that more and more of our older technology, which still works just fine, is getting left behind. Indeed, the computers available today have abandoned serial communications using an RS232 connection. It has been superseded by USB to the point of extinction. Everybody wants faster data flow, with greater inter-connectivity.

And so it would seem that all our investment in RS232 based equipment has been rendered useless. In fact, this is not the case.

Your new computer should have at least one USB serial connector on it, and it is actually a simple matter to get your RS232 equipped balance to talk to your USB equipped computer. Since both USB and RS232 are bidirectional serial communications, you can easily interface the two with a special adapter cable.

You can also install an RS232 serial port card in one of your computer’s expansion slots, but this can be difficult, and most likely an unnecessary exercise.

USB to RS232 adapter cables are available from most reputable scale and balance distributors and dealers, or from your local computer and electronics stores. They are also inexpensive, so they won’t break your budget.

Because USB and Rs232 have significantly different data rates, it is not possible to just change from one connector type to another — they won’t talk to each-other. To accommodate this, part of the adapter cable incorporates circuitry to control the data flow going each way. This prevents data underflows or overflows, which would bring everything to a complete stop. There are other “housekeeping” chores the circuitry manages, as well.

The great thing is many adapter cable manufacturers are able to fit this circuitry into the shell of the RS232 DB9 connector. There are no cards to install your computer, and no awkward dangling boxes. It’s a simple solution to get your balance back in action fast.RS-232 gender changer

Installation is vert straightforward. You just plug the USB connector on the adapter cable into the USB connector on your
computer and plug the RS232 end into the cable from the balance.
Note that standards vary as to which end of an RS232 cable should be female and which should be male. If you need it, be sure to get an appropriate gender changer when you get your USB to RS232 adapter cable.

You may also need a null modem adapter. This swaps the transmit and receive pins when using some types of equipment that don’t swap the pins internally. This is another case where there is no industry standard configuration.

Depending upon which brand adapter cable you get, and which operating system is installed on your computer, you may also need to install a special software driver. The driver is on a CD that is included with the adapter cable, and should include instructions on how to install it.

Some adapter cables don’t require the installation of a software driver if you are using a modern Windows operating system. They take advantage of the plug and play, or PnP, capabilities.

Quality varies greatly between brands of adapter cables (even though they all seem to come from China), and the most expensive one is not necessarily the best. In fact, the one that works best for me is the least expensive on I found.

There are no hard and fast rules to help you pick out the wheat from the chaff, so my recommendation is to ignore the brand names and try one that is at the more economical end of the spectrum and that comes with a software driver CD (in case you need it). The chances are very good that your first choice will work well; if it doesn’t, return it and try another.

You’ll be back in operation in no time at all.

The Secret Life of Batteries | Advice & Tips To Keep Them Running

The Background of Batteries in ScalesScale and Balance Battery

The advent of battery operation in electronic scales and balances has allowed equipment with a wide range of features and capabilities to be portable. Now, electronic weighing equipment with all its wonderful features no long needs to be permanently tethered to an AC power source.

The battery technology found most often in scales is Sealed Lead Acid (SLA), where lead plates are surrounded with a gelled acid electrolyte—sometimes known as a gel cell—or catalyst. The chemical reaction between the lead and the electrolyte generates and stores electricity. And discharging a battery reverses that chemical process. Your car battery works in the same way, except that it is sealed. It can be tipped over, turned upside down, and still works; as long as the case remains intact the acid will not leak.

Some may wonder why scales and balances use SLA batteries rather than the more cutting edge chemistry like nickel metal-hydride or lithium. These pack more electricity in a smaller space, so they could make weighing devices smaller and lighter. The answer is that they are much more expensive, and require a complex charging unit. Lithium batteries must be charged very carefully, because they can catch fire if charging it done incorrectly. SLA batteries, on the other hand, are much more tolerant of charging conditions, so designing and manufacturing a charging circuit is much simpler and less expensive. The also use very mature technology which is widely understood and safe to handle.

battery for scale and balanceBattery Maintenance

SLA batteries require virtually no maintenance; however there are a number of things to take into account to get the most out of them.

First, batteries need exercise just like people. When a device has an SLA battery, it should be used on a regular basis. If a device with a battery is left plugged in, and not going through discharge and recharge cycles, the SLA’s “memory” will learn that behavior and its capacity will be diminished.

Second, when the battery icon lights up, it needs to be recharged. Makes sense, right? If the battery drains too low, it may not recharge, and in some instances it may actually pull down the power in the scale or balance, preventing it from working even when plugged in.

The third thing to keep in mind it that a low battery can make a scale or balance act strangely or inaccurate. When troubleshooting, use a voltmeter to check the voltage: a well charged 6-volt battery will be at least 6.5 volts. Check the voltage with the unit off, then with the unit on. And remember that sometimes a problem doesn’t show up until the battery is under load. The voltage will drop a little when loaded, but should remain above 6 volts. The voltage measurement does not require great accuracy, so an inexpensive volt meter should serve you well.

Fourth, check the connections to the terminals! Make sure they are tight and not frayed or otherwise damaged. Loose connections can limit battery output.

Fifth, make sure there are no loose metal parts floating around inside which could short out the terminals. A batter has a lot of energy which can be very destructive if it all comes out at once.

battery recycleAnd lastly, at the first sign of battery leakage, remove the battery and clean the affected area of the scale or balance. The electrolyte will corrode
almost anything it comes in contact with, such as a metal case, wires, electronic components, and so on. Avoid touching any electrolyte, and wash your hands afterwards. SLA’s are considered toxic or hazardous material, so dispose of the battery properly taking care to contain any leakage; and always recycle.

Things that are not well maintained seem to give out at the worst possible moment. If you take care of your battery, it will give you years of trusty service and not fail when you need it most.

Now, go check your batteries!