The Allen-Bradley 1746-INT4 is an SLC 500 thermocouple/millivolt isolated input module with 4 individually isolated input channels. The isolated input channels on the 1746-INT4 are isolated from the backplane. The 1746-INT4 has 4 light emitting diode (LED) indicators for channel status as well as 5th LED indicating global module status. This device digitally converts and stores analog millivolt (mV) data. The stored data is then accessible to this or any other SLC 500 processor. One 1746-INT4 supports up to 4 thermocouples with paired millivolt sensors. The 1746-INT4 makes use of the Sigma-Delta ADC modulation conversion. The device is rated for 110 milliamps of backplane current at 5 DC Volts. It is rated for 85 milliamps of current at 24 DC Volts. The 1746-INT4 is rated for an overall backplane power flow of 0.6 Watts. The 1746-INT4 uses a low pass digital filter as well as an analog filter. The normal rejection mode of the 1746-INT4 is above 60 decibels (dB) at a frequency of 60 Hertz (Hz) between the terminals.

There is also a separate, common rejection mode. This mode’s performance exceeds 120 decibels between chassis and input chassis ground with 1,000Ω imbalance. This mode offers a total channel bandwidth of 8 Hertz. Field calibration of the 1746-INT4 is mandatory; the calibration must take please a minimum of once annually. The isolation provided by the 1746-INT4 tests at 1000 Volts transient or 150 Volts AC between channel-to-backplane and channel-to-channel. Users can select from an available list of thermocouple input types: B, C, D, E, J, K, N, R, S, and T. The analog inputs offer similar flexibility, ranging from analog inputs of –50-50 milivolts DC and –100-100 millivolts DC.