Rockwell Automation 1734sc-IE4CH E+H Instruments via HART to PlantPAx User Manual - Manual (Page 90)

90 Rockwell Automation Publication PROCES-UM002A-EN-P - July 2014
Appendix B Proline t-mass 65 Thermal Flowmeter
The thermal principle operates by monitoring the cooling effect of a gas stream as
it passes over a heated transducer (PT100). Gas flowing through the sensing
section passes over two PT 100 RTD transducers, one of which is used
conventionally as a temperature sensing device, whilst the other is used as a
heater. The temperature sensor monitors the actual process values whilst the
heater is maintained at a constant differential temperature above this by varying
the power consumed by the sensor. The greater the mass flow, the greater the
cooling effect and power required in order to maintain the differential
temperature. The measured heater power is therefore a measure of the gas mass
flow rate.
Measured Variables
• Mass flow
• Gas temperature
Signals from Instrument to Control System
Signal Details
Current Output Active/passive selectable, galvanically isolated
• Active: 0/4...20 mA, RL < 700
Ω (at HART: RL ≥ 250 Ω)
• Passive: 4...20 mA, Ri ≥ 150 Ω, Umax = 30V DC
Pulse/Frequency Output • Active: 24 V DC, 25 mA (max. 250 mA during 20 msec), RL > 100 Ω
• Passive, open collector, 30V DC, 250 mA, galvanically isolated
• Frequency output: full scale frequency 2...1000 Hz (fmax = 1250 Hz), on/off ratio 1:1, pulse width max. 2s, time
constant selectable (0.0...100.0s)
• Pulse output: pulse value and pulse polarity selectable, pulse width adjustable (0.5...2000 ms)
IMPORTANT If the current output is used as a temperature output, please observe the
information for Class B according to EN 6075.