Choosing a 4-20mA Isolator

Although a virtually straightforward task, selecting an Isolator—specifically a 4-20mA Isolator— involves more than simply comparing the number of channels and the cost per point. Signal isolators receive 4-20mA process current inputs and provide an isolated 4-20mA output signal. On multi-channel units, each channel operates independently and is isolated from the others to prevent interaction between channels. Galvanic isolation eliminates ground loops, reduces, noise, and blocks transient signals.

We have outlined a few concepts to help you specify a 4-20mA Isolator:

• A two-wire system using output loop powered devices is a low cost approach. The I/O modules in this system use power from the output loop to operate and control the 4-10mA loop to the load. This is characterized as a sinking output because the module requires an external power source.
• Without a power source, a 4-10mA Isolator that powers the output loop is required. This type of Isolator is characterized as having a sourcing output. If the I/O module can take power from the input loop to operate and power the 4-10mA output loop to the load, a two-wire system using input loop powered devices is a low-cost approach. Otherwise, a four-wire device must be used.
• To determine if the I/O modules are correctly matched to an application, the voltage level to the external power source must be determined, along with the total input impedance of all loads, and whether other peripheral devices are connected to the input loops.

If you could use some help deciding which 4-20mA isolator is right for you,  contact us. We offer more than 100 modules that interface with a vast array of voltage, current, and strain measuring devices, and they are designed to integrate seamlessly into your existing process.