From a functional standpoint, using an intrinsic safety barrier strictly as a signal conditioner for non-intrinsically safe signals is perfectly acceptable. As long as the field device is able to fully and properly function (meaning that the power requirements for voltage and current are met) when used in conjunction with an intrinsic safety barrier, there will be no harm done to the field device. However, once any non-intrinsically safe device (a device without entity parameters) or non-simple apparatus has been connected with the associated intrinsic safety barrier, the intrinsically safe parameters of said barrier become voided and it cannot be used in any hazardous or intrinsically safe applications any longer.
To avoid confusion when using an intrinsic safety barrier in a non-intrinsically safe application, we always recommend that you order and use green accessory terminals for those barriers. Blue terminals are always used in intrinsically safe applications.
If the intrinsically safe parameters have been voided by connecting a non-intrinsically safe device, we then recommend that some form of defacing be done to the Ex label on the barrier (scratching it out, marking over it, covering it, etc.). The exact form of defacing can be determined by the end user. This is not a required practice; however, it is highly recommended to avoid confusion and potential incidents in the future.