DayTronic 3500 Series, Instruction Manual

Page: 22 / 122

2.a.4 C
ONNECTING A
F
REQUENCY
S
OURCE TO THE
M
ODEL
3540
Fig. 8(a) shows recommended cabling for connecting the Model 3540 Frequen-
cy Conditioner to a pulse transformer transducer with two-wire isolated wind-
ings (tachometer, turbine flowmeter, etc.). Fig. 8(b) shows the connection to a
transistor or logic-circuit driver, while Fig. 8(c) shows the connection to a "zero-
velocity" (i.e., true digital output) sensor. For a single-ended input, note that the
–SIG terminal should be tied to the SIG COM terminal, as shown in Fig. 8(b).
Note too that, when used with an open-collector type sensor—such as a zero-
velocity sensor—a pull-up resistor of typically 10 kilohms is required between the
terminal to which the +SIGNAL line is tied and the +5V terminal, as shown in Fig.
8(c). For a zero-velocity sensor, the +SIGNAL line is to be tied to the +SIGA termi-
nal to eliminate any DC offset (see below).
The Model 3540’s input channel is equipped with a capacitive-coupled input (0.1
µF). This special input may be used with either floating or grounded configura-
tions if you require elimination of DC offset or suppression of high-frequency
noise. Figs. 8(d) and 8(e) show how these effects can be achieved.
Elimination of DC Offset— The 0.1-µF capacitive coupling can be used to elimi-
nate any positive or negative DC offset that exists for the frequency signal. Sim-
ply connect the +SIGNAL line from the frequency source to the +SIGA terminal,
instead of to the SIG terminal (see Fig. 8(d)). The capacitor is here in
series with the +SIGNAL input and allows only AC to pass.
Suppression of High-Frequency Noise— False triggering can sometimes occur,
especially at the low-frequency input range, because of stray pickup of frequen-
cies outside the common-mode range. Capacitive coupling of the frequency
input to ground can in such cases serve to suppress unwanted signal noise.
Thus, if you find your frequency reading to be unacceptably unstable or "noisy,"
you should tie the +SIGA terminal to the SIG COM terminal, while maintaining the
SIGNAL connection to the +SIG terminal (see Fig. 8(e)). With reference to
the suppression of high-frequency noise by groSIGA, note that
• it is always recommended for magnetic-pickup sensors; and
• in general, it is NOT to be used with transducers that produce
active output (e.g., TTL logic drivers).
2.4
2
S
ETUP
: C
ONNECTIONS AND
P
OWERUP
2.a T
RANSDUCER
C
ONNECTIONS
: M
ODEL
3540
–
SIG
+
SIG
CNTR
WIRE
+
SENS
+
EX
LVDT INPUT
–
EX
–
SENS
HI –
SIG
HI +
SIG
–SENSE
+SENSE
+EXCITATION
+SIGNAL
–EXCITATION
SHIELD
–SIGNAL
10K
10K
N/C SHLD N/C
Fig. 7(d) Model 3530
Transducer Cabling: 5-Wire Variable
Reluctance Cabling (20 ft. or longer)