Using OSI Watt Transducers on Variable Frequency Drives

Line HarmonicsPC5, K can

 The line waveform of variable frequency drives, “VFD’s,” can be severely distorted by voltage harmonics created by the drive and can cause erratic operation of equipment connected to these lines. Special attention should be paid in selecting and installing transducers to monitor these variable frequency drives.

Ohio Semitronics, Inc. offers two models of watt transducers for monitoring VFDs, the PC5 series and the P series. The PC5 series should only be used on the line side ahead of the VFD while the P series can be used either in front of the drive or between the drive and the load.

Recommendations in Selecting and Using Transducers for VFDs

  1. The PC5 series as indicated should only be used on the line side in front of the VFD. Also, select or use only externally powered models such as the PC5-___B, D or X5. Internally powered models, options A, C or CX5 can create problems since the internal power supply is connected directly to the distorted line voltage.
  2. Another problem can exist if you are using the 1mA output, option B with the PC5. The VFD can cause noise on this output option. It is recommended to use option BX680 which is a grounded 0-1mA output to eliminate this problem.
  3. The P series transducer was designed to work on VFDs, although precautions still must be taken as indicated in section 4.
  4. Installation
    • Mount the transducer as far away from the VFD as possible, preferably out of the VFD enclosure and in its own steel enclosure.
    • Ground the transducer’s metal case to earth ground and use star washers with mounting screws when mounting.
    • Route all transducer wires away from the VFD lines and twist together the voltage lines.
    • The output signal leads should be as short as possible, using only a shielded twisted pair, with the shield connected at the monitor’s chassis ground only.VFD
    • Use only transducers which have a separate input for instrument power. Connect the instrument power to a clean 115 Vac 60 Hz power source. Use an RFI line filter on the instrument power input if available.



Extending Current Transformer Lead Lengths

Leads on most OSI current transformers can be extended, but to maintain accuracy there are a few conditions to consider.

How far can I extend the lead? How do you tackle extending a lead length? Using the chart and examples below, a better understanding to these questions can be gained.

ECT (D-size) spec sheet image, cut out

ECT- (D size)

How to Determine Maximum CT Lead Length

The capacity of a current transformer to drive a load is specified in units of VA (Volt-Amps). The amount of energy required to energize a load is also specified in VA.  For a current transformer to be able to drive a load and maintain specified accuracy, the VA rating of the current transformer must be equal to or greater than the VA required to drive the load.

I.e. VA (CT Rating) ≥ VA (load)

If the VA rating of the CT is greater than what is required to drive the load, then the extra VA can be used to drive the load of added CT wire length. The following table shows how many feet of additional wiring (by wire ga.) can be driven per the CT’s extra VA rating.



Further questions about determining maximum CT lead length? Contact OSI at 1-800-537-6732 or visit and check out our chat feature.

10 Things That Take Place at an OSI Product Training: Partnership with Camille Bauer

Camille Bauer Metrawatt AG, located in beautiful Switzerland, partnered with OSI last week to conduct “product training”. Now wait, it is not as monotonous as it sounds. OSI’s passionate and dedicated friend Ron De Winter from Camille Bauer, partnered with OSI’s very own Ansul Robb, Cory Forler, Dominick Piccinich, and Jim Babcock (The dedicated, knowledgeable, and friendly sales and technical staff of OSI) to discuss, teach, and learn about the Sineax DM5 series, Sineax AMx000 series, and the A series among many others. Here are 10 things that happened.

Power Points

We’ve all been there. It is hard hard to do any type of training without a one-to- many communication platform, so of course Power Point presentations were present during our Camille Bauer Training. The decks were detailed, informative, and engaging however, as most know, it is not each slide that keeps you awake, it is the presenter. Ron De Winter is hilariously and dangerously knowledgeable and he is a huge reason Camille Bauer training’s are so successful.


The answer is no, Ron did not talk AT the crew for three days straight. There was interaction that brought on helpful, informative, and intriguing conversation. Cory, Jim, Dominick, and Ansul all contributed to the conversation and with each discussion came questions.


Nine times out of ten there are questions that result from a discussion, duh. In an OSI and Camille Bauer product training, no one is afraid to ask for clarity. The questions came from both sides of the conversation, OSI’s side, and from Ron’s side (Camille Bauer). In result, the knowledge depth for every discussed product was widened.


At OSI, the “what if” is asked. No idea is pushed under the rug, especially in product training. Ideas are placed on the table to benefit the future of electrical engineering, and our customers’ electrical projects. The best way to provide solutions is to first recognize a new idea.

Customers’ Voice

There were customers at product training? No, however every discussion, description, and question was balanced around the customer. How can we provide solutions if we do not think like the customer? We skip the obscure, and place our priority, the customer, at the forefront of each training. How will this benefit our customers? Is the product solving what they are asking us to solve? Will it measure what we want it to measure? How will this training help me help them?

Product Visuals

Unless you work up close and personal in manufacturing, and your life is not solely focused on making phone calls and writing emails, it is not every day that you get to see, touch, and study a transducer. Days before Ron’s arrival, he sent his Camille Bauer products to the US so that they could accompany training. Sure, you could post a connection diagram on a power point slide, or post a picture of a power meter, but what fun is that? The fun, and especially the knowledge, comes from hands on activity.

Hands on Training

On training day number one, after a long lecture and discussion about the Sineax DM5 series, Ron took a seat and Cory (Senior Product Support Coordinator) placed himself at the front of the training room. Why? The answer is to expand his already existing knowledge of CB Manager, and to spice up the dynamic of the training. A little untraditional in terms of a “product training” but it is hard to say that OSI is a traditional manufacturer. The roles were reversed and Cory began to explain CB Manager for the DM5. OSI does what needs to be done to be the most knowledgeable. This was true hands on training because the student became the teacher and Cory vastly expanded his knowledge of CB Manager by doing rather than listening.

Software Demonstration

How does OSI as a company teach you to use CB Manager without the physical products and software being present? The answer is we don’t. The point here is, if you buy from OSI,  Cory, Ansul, Jim, and Dominick have already learned CB Manager and can help you learn it for your newly purchased product.There is no need to learn CB Manager all on your own. Here at OSI, we consider ourselves to be resources, and we ask that you, our customers, take advantage.


At this point in the blog, it is impossible to assume that the Camille Bauer Training was only about technology. It is not every day that you get to learn about a different culture from your own, unless you study it in school, or travel the world twice a week. Many individuals this week at OSI enjoyed a great piece of chocolate from Switzerland and others got to enjoy dinner with Ron and discuss what it’s like to live in a beautiful place like Switzerland. This being said, it is always an exciting time when Ron visits because OSI gets to eat great chocolate and learn about a culture that many have not been exposed to.


So you’ve noticed OSI consumed some chocolate last week. Yes, yes we did. Camille Bauer training’s are not a “learn then leave” type of training, they are fun. We laugh, joke, and enjoy the company of those who surround us. Honestly, product training’s here at OSI would not be effective without a little bit of fun.


Questions about OSI products or our partnership with Camille Bauer?
Contact us at 1-800-537-6732 or visit


OSI Has Chat! Website Update

We (Ohio Semitronics, Inc.) currently have over 14,000 products listed on our website. We have so many power measurement options that sometimes it is hard to know where to begin. A customer could search through pages and pages of products or they could call our sales staff, and discuss what they need over the phone. However, the problems with “calling in” are plentiful, and each individual customer has their own reason as to why chat would work much better for them. In response to the many benefits that a chat feature would give to our customers we launched one and it is now live! By implementing this chat feature on to our website, we are providing our customers with one more way to meet their power measurement needs.


Here’s how it works

When you’re on any page of our website, you will see an icon to the right of the page that says “Live Chat”. This means that someone at OSI is logged on and is available to answer your questions. As we’re still learning and discovering all of the possibilities of this new chat feature, the positioning of the “Live Chat” button may change, but it will never go away. Once you have clicked on the button, it will ask you to type in your message and begin the live chat.

Something to keep in mind is the timing of your visit to our website. When no OSI representative is logged into the chat feature, the button will look a little different. The button will no longer say “Live Chat”, it will say “Contact Us”. From here, fill out the contact from and leave your message. An OSI representative will more than likely get to your message the following business day, or within the hour if it is around noon (eastern time).

We are very excited about this new addition to our website, and we hope that you will take advantage of the Live chat’s easy to use, and resourceful functionality.

Happy chatting!

Ohio Semitronics, Inc.

Chat capabilities provided by: Live Agent

Example of Power, Voltage, and Current Monitoring

The following text describes monitoring voltage, current, and power delivered to a test load; the load in this example is a domestic kitchen refrigerator.

Transducers used:
ACT-010A current transducer is wired in series with the load.
AVT-150A voltage transducer is wired in parallel with the load.
PC5-010A is wired in series with the load for monitoring the current and in parallel with the load for monitoring the voltage.

The former transducers are examples. One other transducer that may be used includes the multifunction board level transducer, PTB. This board provides analog outputs proportional to each phase of true RMS.

This example uses digital meters, such as a 15660, which are scaled using precision load resistors.


Load resistors are selected as follows:

  • Remember Ohm’s Law (R=V/I) where R is the resistance in ohms (Ω), V is the voltage that we want to apply to the digital meter, and I is the current from the transducer.
  • The ACT-010A provides an output of 1 mADC at 10 amperes AC through terminals 3 and 4. 1 mADC represents 10 amperes AC. Adjust the decimal point of the digital meter so that it displays 10.00 with 1 mADC through 1000Ω load resistor.
  • The AVT-150A provides an output of 1 mADC at 150 volts AC applied to terminals 3 and 4. 1 mADC represents 150 volts. Adjust the decimal point of the digital meter so that it displays 150.0 with 1 mADC through 15000Ω load resistor.
  • The PC5-010A provides an output of 1 mADC at 1000 watts. 1 mADC represents 1000 watts. Adjust the decimal point on the digital meter so that it displays 1000 with 1 mADC through the 1000Ω resistor.

Now all three meters are scaled correctly and may be labeled amperes, volts, and watts. Note that the power does not equal volts times amperes (V*A). This is because the refrigerator has a power factor of 0.866 which is normal for older refrigerators. For the single-phase situation, power factor may be determined by dividing the power reading by the product of volts and amperes.

Call Ohio Semitronics, Inc. today, 1-800-537-6732

Selecting and Using Transducers Series: For the Measurement of Electric, Power, Voltage, and Current

Voltage Transducers

What is a voltage transducer? Voltage transducers provide a DC (direct current) or voltage output directly proportional to the AC input voltage. AC voltage transducers typically have a transformer input to isolate the transducer from the voltage input.

Voltage Transducer

Following the transformer are the electronics.

 There are two types of AC voltage transducers.

  1. Absolute average measuring, RMS calibrated (or mean value measuring, RMS calibrated).

These inexpensive transducers simply convert the AC input to DC and have the output calibrated to represent the root mean square (RMS) value for sine wave input. This type is very adequate for situations in which the voltage wave shape is not distorted. Any odd harmonic or discontinuity will introduce large error. Use the true RMS measuring type when distortion of a sine wave is present such as Variable Frequency Drives and SCR controlled loads.

  1. True RMS (Root Mean Square) measuring.

These transducers calculate the RMS value of the voltage input and provide a DC output directly proportional to the effective value of the voltage input. This type should be used whenever the voltage is distorted. Transducer models are available for nominal input voltages of 69, 120, 240, and 480 volts. These typically have a measuring range of 0 to 125% of the nominal input rating. Thus a 120-volt model has a range of 0 to 150 volts. For voltage input higher than 600 volts, one should use a potential transformer.

Need more help selecting the best and most accurate power measurement tool for your project? Call Ohio Semitronics, Inc. today, 1-800-537-6732