Table of Contents
Advertisement
Technical description
3.1
CIRCUIT ANALYSIS
R. F. Power Meter TF 2502 consists of an in-line thermocouple detector, a
diode detector and a terminating load as shown in Fig. 3.1.
IN-LINE DETECTOR with THERMO-ELEMENT
L~------~~'~"-A_D------~--.
;
~
TC1
THERMOCOUPLE
M2
lWATTSl
Fig. 3.1
Functional diagram
of
r.f. power meter
A smallpercentage of tlie incident power is absorbed by the heater of the thermo-
couple and the resultant rise in temperature is monitored by a series of bimetallic
junctions, TCl.
The
thermo~electric
e. m. f. thus produced is then measured by a
d. c. millivoltmeter, M2, calibrated in terms of total power in watts.
Power applied to the thermo-element produces a current, I, in the heater
resistance, R5, with a resultant heat dissipation of I2R5.
The thermocouple output
voltage is consequently proportional to 12 since its e. m. f./ temperature response is
nearly linear.
Hence the detector gives a d. c. output proportional to true mean
power, and independent of the waveform of the power.
The input voltage is sampled by a capacitance probe, rectified by diode MR1
and monitored by meter M1 which has an arbitrary 0-100 calibration.
Potentiometer
RV3 adjusts the sensitivity of the meter.
This circuit gives a fast-response indication
and also provides a demodulated output at the MOD OUT jack, JKA. for external
monitoring.
2502 (1)
13
Advertisement
Table of Contents
