The T798 is a Highway Addressable Remote Transducer (HART) based temperature transmitter that can be factory or field configured using an optional 1 or 2 line alpha-numeric display, optional PC based software and cable. Alternatively an HC275 Hand Held Communicator loaded with the T798 Device Description from the Hart Foundation Library can be used.

The T797 is a programmable temperature transmitter that can be factory or field configured using the same optional 1 or 2 line alphanumeric display as the T798.

Both the T798 and T797 accept a wide variety of thermocouples (B, C, E, J, K, L, N, R, S, T, U & special) and 2-wire, 3-wire, or 4-wire Platinum RTDs (DIN alpha = 0.00385, SAMA alpha = 0.003923 and special) as well as millivolt (mV) and resistance inputs. They provide an isolated 4- 20mA output loop that is proportional and linear to the desired temperature input range. The factory can configure custom curves and accommodate other input types including 10 Ohm Copper and 120 Ohm Nickel RTDs.

Programming via HART

Utilizing the HART protocol, the T798 can be accessed and programmed for dual two-wire RTD or dual thermocouple measurement; transmitting or displaying differential or average temperatures. For RTDs secure or independent dual RTD measurements can be made. Other functions can be set using Hart, such as input dampening, burnout detection, fail-safe report (sensor or transmitter failure produces over or under output range condition), loop test (manual control of output current), line frequency filtering, smart smoothing (filters small changes but reacts quickly to large changes), internal temperature, cold junction temperature and display or transmitter identification (e.g. display label, tag ID, descriptor, message, sensor serial number, configuration date, etc.).

Configuring via Display

For quick and easy configuration the optional one line and two line alphanumeric displays (model T79D-1 and T79D-2) are useful for setting up and trimming the 4-20mA output or display reading to correct for sensor errors. These displays provide a 4 digit reading of the temperature (e.g. 2345, 234.5, 23.45) and will alert the user in the case of sensor failure or burnout for both RTDs and thermocouples by flashing ‘fail’ and ‘safe’ sequentially.

Linearization:     

Thermocouple and RTD linearization to ±0.05°C. Custom linearization with 22 pt curve (consult factory).

Input Impedance:   

Greater than 1M Ohm

Output:     

Analog, Two-wire 4 to 20mA

Transmitter Accuracy:   

±0.05% of the millivolt or ohm equivalent input reading, or the value from the Accuracy Table, whichever is greater; plus ±0.05% of the span. For thermocouples, add ±0.5°C (0.9°F) for cold junction effect. Accuracy includes transmitter repeatability, hysteresis and linearity as well as ambient temperature effect. A/D conversion error, analog output error, line voltage effets, humidity effect under non-condensing conditions and vibration effect to 2g's & 500 Hz.

Transmitter Repeatability:   

One-half the transmitter accuracy

Cold-Junction Compensation:   

Digital self-correcting over the ambient temperature range to within ±0.5°C

Output Ranging Adjustments:      
Analog Zero: 100% of Sensor range (Non-interacting)

Analog Full-scale:

Normal or Reverse Acting Ambient

Temperature Stability: 

Self-correcting over operating temperature range

Long Term Stability: 

Deviation per year is less than: 0.025% of the output span ±0.05% of the reading)

Damping: 

Factory selectable constant (63%) from 0 to 32 sec.

Failsafe:     

User settable to 3.6 or 23mA

Operating Temperature Range:      

• Electronics: -40°C to +85°C, -40°F to +185°F 
• Display (full visibility): -20°C to +70°C, -4°F to +158°F
• Display (with reduced visibility): -40°C to +85°C, -40°F to +185°F
• Storage Temperature Range: -50°C to +85°C, -58°F to +185°F
  

Mounting Position:   

No effect on measurement value

Weight: 

• T787: 6 oz. 
• T79E-O/D: 21/2 lbs. 
• T79E-1: 12 oz.
  

Isolation:     

500VAC Input to Output