What is a CT? Current Transformer or Current Transducer?

What is a CT? Current Transformer or Current Transducer?

This article stems from an argument over what CT stands for. But before we can determine what CT stands for, we need to understand what a current transformer and a current transducer are.

Current transformers are used for measuring energy consumption on the power grid. A current transformer is similar to any other transformer. It is has a primary winding, a magnetic core, and a secondary winding. The primary winding will usually be a single turn and the secondary winding will be 10s or 100s of turns. Then by coupling the primary and secondary windings the amperage on the secondary winding will be proportional to the primary winding.

For example, most current transformers are sized for a secondary current of 1 amp or 5 amps. If you have a current transformer that is 1000:5 then that means that 0-5 amps on the secondary will be directly proportional to 0-1000 amps on the secondary. So if you have 0 amps on the primary you will have 0 amps on the secondary, if you have 250 amps on the primary you will have 1.25 amps on the secondary, if you have 500 amps on the primary you will have 2.5 amps on the secondary, and if you have 1000 amps on the primary then you will have 5 amps on the secondary. Current transducers can be extremely dangerous and can kill you since an open secondary can produce voltages 100s or even 1000s of times higher than the primary.

A current transducer looks almost identical to a current transformer. We see these used more in industries where we are monitoring motor or heater loads for example. It has built in circuitry to generate a low level DC signal base on the AC amps. This will usually be an analog 0-5VDC, 0-10VDC, or 4-20mA signal and will occasionally be a pulsed output where the frequency of the pulse is proportional to the amps going through the transducer.

As far as what does a CT stand for, I don't think there is a well defined answer. Like any acronym, it can stand for many things and you must look at the context it is being used in to determine whether someone is talking about a current transformer or a current transducer. Also, many people use the terms interchangeably and while I don't think we need to correct them, it is important that you understand that they are two different devices when selecting one for an application.