Omega TX91 manual Introduction

Introduction 1

The TX91 has reverse supply polarity protection and will operate with a wide range of supply voltages (11 to 44VDC). It has an input sensor break-protection circuit that forces the output current to go upscale when the thermocouple wire opens. It also is provided with a screw terminal, where the output current can be measured without interrupting the power loop. The TX91 does NOT provide isolation between its input and the 4-20 mA output; therefore, an undergrounded thermocouple junction is suggested to prevent possible ground loops.

Note that most thermocouple transmitters with 4-20 mA outputs, including the TX91, are proportional with respect to the thermocouple input voltage. However, the relationship between temperature and millivolt for all the thermocouple types is somewhat non-linear. This leads to maximum error at approximately the midpoint of the range as

05 shown in Figure 1-4.