English
Connection of a single-balanced loop (input) is shown in the following diagram.
The ALARM contacts (the output is open on the detector activation) and TAMPER (the conact is switched off when there is a sabotage attempt) are always NC - i.e. the switched contact represents the idle state.
The idle state is always transmitted into the system as a log. "0" (though it actually means a switched contact of the detector!).
The loop resistance:
|
The state |
A typical value |
Permitted range |
ALARM contact |
TAMPER contact |
|
Idle state |
0 |
0 ÷ 1250 Ω |
switched |
switched |
|
Activation |
2k2 |
1,750 ÷ 2,500 Ω |
open |
switched |
|
Sabotage |
∞ |
> 7 kΩ |
x |
open |
Fig. 1. The basic connection of the circuit of a single balanced loop
Notes:
-
The loop resistance is measured by the relevant module input, and the module evaluates the measured value and transmits two binary variables, ALARM (the idle value corresponds to log "0") and TAMPER (the idle value corresponds to log "0").
-
The values of the resistors have a tolerance band of approx. 10 %, to avoid a problem of bad evaluation resulting from a higher tolerance value of resistance, or fluctuation of the resistance value, e.g. due to temperature.