The new version flowmeter has two methods for thermal energy measurement;
●Utilize temperature transmitter with 4-20mA output. The temperature analogue signal can be inputted by terminals AI4 and AI5 of the flowmeter. If possible, we recommend PT100 resistors which can have a better performance.
●Utilize standard 2-way PT100 resistors. Its temperature range is 0-150℃, and after calibration, the accuracy in the range of 0-150℃ is less than 0.1℃.
New generation ultrasonic flow meters have two specific heat value methods in system software: one is GB, standard CJ128 specific heat value(factory default),under this setting, the flow meter will calculate the enthalpy of water based on the international standard; the other is 1. Fixed Specific Heat, if the fluid is other than water, users should select option ‘1. Fixed Specific Heat’, and enter the specific heat value of the fluid. If the temperature is over 150℃, also use this method.
Because specific heat of water is different in different temperatures, the measuring results with two methods above are also different. Generally, the result in the first method is smaller than that from the second method.
1) With fixed specific heat value method
qh=qV×C×(tS-tR)
Here:
C: Specific heat value of water, the value can be input in M86
tS: temperature of water supply
tR: temperature of water return
Heat totalizer: Q=Qn+qH×△t
△t=0.5second, which means totalizer time is 0.5s.
In window menu M8., users can select installing point: water supply direction or water return direction.
The factory default is water supply installing and GB, standard CJ128 specific heat value.
2) With specific heat value method
While flow transducers installed on water supply pipe, the formulation is as below:
Instantaneous Heater rate qh=qV×pS×(hS-hR)
While flow transducers installed on water return pipe, the formulation is as below:
Instantaneous Heater rate qh=qV×pR×(hS-hR)
Here:
qV: instantaneous volume flow rate
pS: density in water supply temperature
pR: density in water return temperature
hS: specific heat value in water supply temperature
hR: specific heat value in water return temperature