8.7.1 Impedance of proportional output 8.7.1.1 Procedure
Select the setting at which the gain controls are in the middle of their range, and the widest band setting of the equipment.
Adjust the trigger of the measurement signal so that a measurement signal, with the carrier frequency fo
measured in 9.5.2, is produced with every transmitted pulse.
Set the amplitude of the measurement signal to produce an indication at 80 % of screen height and measure the output voltage Vo. Terminate the proportional output with a resistor of value Rl which satisfies the following condition:
max
max 0,85
75 ,
0 I
R I V
l o≤
≤ (8)
where
Imax is the maximum current that can be driven by the proportional output.
Record the altered output voltage Vl. The (resistive part of the) output impedance is calculated using
l l
A o R
V
Z V
−
= 1 (9)
8.7.1.2 Acceptance criterion
The measured output impedance shall be within the tolerance quoted in the manufacturer's technical specification.
8.7.2 Linearity of proportional output 8.7.2.1 Procedure
Select the setting at which the gain controls are in the middle of their range, and the widest band setting of the equipment, adjust the triggering of the measurement signal so that a measurement signal is generated with each transmitted pulse. Adjust the amplitude of the measurement signal to give an indication at 80 % of screen height, and measure the voltage at the proportional output, calling this the reference voltage. The output voltage for full screen height (FSH) is 1,25 times the reference voltage.
The amplitude of the measurement signal is changed in steps according to Table 3.
The deviation of the output voltage from the nominal value is recorded.
Table 3 — Expected output voltage for specified attenuator settings Attenuation
dB
Nominal Value
% of FSH output voltage
+ 1 90
0 80
- 2 64
- 4 50
- 6 40
- 8 32
- 10 25
- 12 20
- 14 16
- 16 13
-18 10
8.7.2.2 Acceptance criterion
The measurement shall be within the tolerance quoted in the manufacturer's technical specification.
8.7.3 Frequency response of proportional gate output 8.7.3.1 Procedure
This test measures the response of the proportional output to the frequency of the receiver input signal. The measurement set-up in Figure 8 is used whereby a measurement signal is generated with every transmitted pulse.
Set the calibrated gain control to the mid position and the non-calibrated control to maximum gain. The frequency fgmax for maximum output is found by varying the carrier frequency of the measurement signal until the FSH voltage is obtained at the analogue output. Once fgmax has been found, adjust the amplitude of the measurement signal so that the output voltage is 80 % of the FSH voltage found in 8.7.2. After this, the carrier frequency of the measurement signal is reduced and increased until the output voltage drops by 3 dB.
The values fgu, fgl are measured. Using fgu and fgl, the centre frequency fgo is calculated according to:
gl gu
go f f
f = × (10)
and the frequency bandwidth ∆f is calculated according to:
gl gu
g f f
f = −
∆ (11)
8.7.3.2 Acceptance criterion
The measurement shall be within the tolerance quoted in the manufacturer's technical specification.
8.7.4 Noise on proportional gate output 8.7.4.1 Procedure
Terminate the receiver input with 50 Ω. Set all gain controls to the maximum value and use the widest band on the equipment. The output voltage shall not exceed 40 % of the FSH output. Otherwise, the gain is to be reduced so that 40 % of the FSH output voltage is not exceeded. The gain setting is to be recorded.
8.7.4.2 Acceptance criterion
The measurement shall be within the tolerance quoted in the manufacturer's technical specification.
8.7.5 Influence of the measurement signal position within the gate 8.7.5.1 Procedure
Use the set-up shown in Figure 8 to generate a measurement signal for each transmitter pulse. Select a mid gain position and the widest band setting on the equipment. Adjust the amplitude of the measurement signal, of the centre frequency fo, to produce an indication at 80 % of screen height. Position the measurement signal in the first fifth, centre and in the last fifth of the gate and measure the voltages of the analogue output.
8.7.5.2 Acceptance criterion
The measurement shall be within the tolerance quoted in the manufacturer's technical specification.
8.7.6 Effect of pulse shape on the proportional gate output 8.7.6.1 Procedure
Pulse transfer is characterized by the response of the amplifier to different measurement signals.
Use set-up in Figure 8 to produce a measurement signal with each transmitter pulse. Select mid gain and the widest band setting on the ultrasonic instrument. Set the carrier frequency of measurement signal to fo, as measured in 9.5.2 for the selected filter. Adjust the amplitude measurement signal so that the voltage at the output of the proportional gate is 80 % of the FSH output voltage.
Using the test signals given below, note the external attenuator setting required to bring the output voltage to 80 % of the FSH output voltage:
a) single sine wave with a negative leading edge;
b) single sine wave with a positive leading edge;
c) measurement signal with five periods, similar to Figure 7;
d) measurement signal with fifteen periods, similar to Figure 7.
8.7.6.2 Acceptance criterion
The measurement shall be within the tolerance quoted in the manufacturer's technical specification.
8.7.7 Rise, fall and hold time of proportional gate output 8.7.7.1 Procedure
Using the measurement set-up in Figure 8, adjust the measurement signal trigger so that each transmitter pulse generates a measurement signal. Also use a mid gain setting and the widest band setting of the equipment and a measurement signal with a carrier frequency fo, as measured in 9.5.2. Adjust the measurement signal so that 80 % of the FSH output voltage is obtained at the proportional gate output.
Change the trigger of the measurement signal so that at the analogue output, the minimal output voltage can be observed between two consecutive output signals (e.g. for one transmitter pulse with a measurement signal there follows approximately one thousand transmitter pulses without a measurement signal). The rise time is the time interval in which the output voltage rises from 8 % to 72 % (see Figure 9) of the FSH output voltage (this being equivalent to 10 % and 90 % of the output signal generated by the measurement signal).
The fall time is the time interval in which the output voltage falls from 72 % to 8 % of the FSH output voltage (see Figure 9). The hold time is the time interval in which the output voltage is above 72 % of the FSH output voltage following the end of the test signal (see Figure 9).
8.7.7.2 Acceptance criterion
The measurement shall be within the tolerance quoted in the manufacturer's technical specification.