THM1176/TFM1186 Use
r’s Manual
v 2.0 r 1.0
– 02/20
Copyright © 2020 Metrolab Technology SA
www.metrolab.com
10
More details on the single-chip 3-axis Hall sensors can be found in Chapter 7-
THM1176-MF/HF/HFC Sensor Details.
3-3 MEASUREMENT PROCESS
•
The analog sensors measure the three vector components of the magnetic
field and the sensor’s internal temperature.
•
At the input of the electronics, the inputs from the sensor pass through a 1
kHz anti-aliasing filter. This 2
nd
-order filter is designed to be flat to 1 kHz;
the -3 dB point is at several kHz.
•
A multiplexer selects each of the inputs in turn and routes the signal to a
16-bit ADC.
•
A microprocessor (µP) receives commands from the host computer,
controls the measurement process, and returns the data to the host.
•
To reduce noise, the µP samples each field component several times,
depending on the degree of averaging (oversampling) specified by the
user. The sample rate is as fast as possible
– in practice just under 10 kHz.
•
With this oversampling, the signals are sampled in the following order:
B
x
, B
x
, B
x
,
…, B
y
, B
y
, B
y
,
…, B
z
, B
z
, B
z
,
…, T
where T is temperature.
•
The averaged field measurement [<B
x
>, <B
y
>, <B
z
>] is then stored in the
acquisition buffer, as one measurement point. T is averaged with the
temperature measurements for the other points in the acquisition buffer.
•
The µP then waits for a trigger before starting the next acquisition. The
trigger can occur immediately, at the expiration of a timer, or at the
reception of a USB trigger command, as specified by the user.
•
The µP accumulates measurement points in the acquisition buffer, up to
the number specified by the user
– the so-called “block size”. The
maximum block size supported by the µP is 4096 measurement points. The
acquisition is actually double buffered, to allow the acquisition to continue
while data is transferred to the host computer.
•
At the end of each block of measurement points, the µP records a 64-bit
time stamp, accurate to 167 ns. It is up to the software to reconstruct a full