6. Transducer Sensitivity (M72Ax / M72S1)
The output voltage of the M72Ax and M72S1 instruments can be scaled to result in a decimal
ratio between the output voltage and the mechanical measurement quantities, for example
100 mV/ms
-2
or 1 V/Pa. By this means a measuring chain will always yield the same output
voltage per mechanical unit, independently of the sensor type.
To ensure these results the transducer sensitivity, also called the transfer factor, is required. In
the case of accelerometers with charge output this is the charge transfer factor B
qa
, and for IEPE
accelerometers it is the voltage transfer factor
B
ua
.
The charge transfer factor is stated on the
calibration certificate or the sensor data sheet.
The transducer sensitivity can be entered in two ways:
1. Manually: to enter the sensitivity manually press ▲ or ► to switch from the modulation
display to the sensitivity display. By pressing the button ► again the decimal point moves
position. Press ▲ to increase the digits left of the decimal point by one. Enter all four sensi -
tivity decimals consecutively. After this, position the decimal point to the right by pushing
the button ►.
2. Automatically: when connecting a transducer with an electronic data sheet (TEDS) to IEEE
1451.4 (Templates 25, 27 or 28), the sensitivity is read automatically and appears briefly on
the display.
The most recently entered sensitivity can be viewed at any time by a short press of ▲ or ►. It is
also saved when the instrument is switched off.
By entering the sensor sensitivity (B) the selected gain (G) of the M72 is multiplied by a correc -
tion factor (K). The total resulting gain (G
tot
) is:
G
tot
=
B
⋅
K
⋅
G
The correction factor (K) is calculated from the entered transducer sensitivity. In this calculation
the decimal point is moved to give a numerical value of between 1 and 10. Then the reciprocal
value is calculated. For this reason, the correction factor can only take values in the range of
0.100 to 1.000.
Consequently, the entered position of the decimal point for the sensitivity has no effect on the
gain. The decimal point only provides the entry position and displays the transducer sensitivity.
Even leading zeros have no influence. In this way, for example, the input of “2.570” results in
the same gain as “025.7”
.
It is nevertheless important to enter all known decimals.
Of most relevance to the user is the ratio between the output voltage and the measured mechani-
cal quantity. For example:
The sensitivity of an accelerometer is B
qa
= 18.25 pC/ms
-2
. The selected gain is V = 100 mV/pC.
The calculated correction factor is
K
=
1
1,825
=
0,5479
Thus resulting in the total gain of:
G
tot
=
18.25 pC
/
ms
−
2
⋅
0.5479
⋅
100 mV
/
pC
=
1000mV
/
ms
−
2
Upon switching the input type the sensor sensitivity is reset to 1.000.
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