DSP-10 User Manual
Page 8 of 26
DSP10_MAN_C
Fail-Safe vs Fail-Secure
Here’s a little note on fail-safe versus fail-secure operation. On the DSP-10, the option for fail-safe or fail-secure
only applies to the A output. In general, a fail-safe detector will activate the output when the loop circuit is
failed. This is useful on a safety loop to prevent accidental closure of a gate arm on a vehicle. On the free exit
loop this will keep the gate open until the situation is fixed. Fail-safe is used in applications where it is important
to allow traffic flow to continue. A fail-secure detector will not activate the output when the loop circuit is
failed. This will keep the gate closed. This is useful in high-security areas or installations where containment is
needed.
The B output is always fail-secure when not in the fail output mode.
The DSP-10 is one of the few vehicle detectors that honors fail-safe and fail-secure even in the absence of
power. Inside the unit, on the main PC board, are three jumpers that set the failure mode. When placed in the
fail-safe position, the A output relay will be fail-safe in the absence of adequate voltage. If placed in the fail-
secure position, the reverse is true. The jumpers are factory set to be fail-safe. All three jumpers must be set to
the same setting. Not doing this will cause incorrect operation of the A output.
Sensitivity
The detector has ten user selectable sensitivity levels. In most situations the medium sensitivity 5 setting will
work effectively. For those situations where setting 5 is not sensitive enough, raise the sensitivity one level at a
time until the desired performance is obtained. For those situations where the detector is oversensitive, lower
the sensitivity one level at a time until the desired performance is obtained. The sensitivity is factory set to 5.
Like most inductive loop vehicle detectors, the DSP-10 directly measures the change in frequency of the loop
and from there, calculates the change in inductance when a vehicle interacts with it. The change in inductance
is measured as %ΔL/L (reads as “percent delta L over L”).
For the ten sensitivities, the thresholds are:
Setting
Sensitivity
Setting
Sensitivity
0
.48% ΔL/L
5
.08% ΔL/L
1
.32% ΔL/L
6
.06% ΔL/L
2
.24% ΔL/L
7
.04% ΔL/L
3
.16% ΔL/L
8
.03% ΔL/L
4
.12% ΔL/L
9
.02% ΔL/L
Frequency (DIP Switches 9 and 10)
Another important variable is loop frequency. When loops are installed sufficiently far apart, any two loops will
not interfere with each other. However, if two loops are fairly close together, say two to four feet apart, the
inductive fields may couple together and may interact causing intermittent false detections. The two main
variables for inductive coupling are distance and frequency separation. To aid in avoiding inductive coupling,
each DSP-10 unit comes with two frequency switches. They are binary coded allowing up to four different
