Issue
Since the introduction of Integrated Access Control and the ability to monitor Supervised Inputs, Technical Support Services has received many inquiries on how to make supervised DI/DA points work in I/NET 7700. Questions range from "Can I run the wire 100 feet or 300 feet? Do I use 1% resistors or 5% resistors? Some of the controllers are more flexible than others with respect to these issues. Since there are many variables which affect the operation of supervised inputs, this document should give you enough information to make DI/DA supervised points work in almost any situation.
Environment
- Supervised Input
- High Security Areas
Cause
There are 3 basic categories of I/NET 7700 controllers in regards to how they handle the supervision of inputs. The first group consists of the 7716 PCU, 7718 PCU, and 7756 PCU. The second is the DPU 7910, DIU 7930, and the DIO 7940. Finally the DPU 7920 is in a group by itself. None of the other CSI controllers were designed to handle supervised inputs. What distinguishes these groups is that they require different voltages to change from one state to the next.
Resolution
The following (Table 1) lists what voltage each controller expects to see at its input terminals in order to report the correct state.
| 7716, 7718, 7756 | 7910, 7930, 7940 | 7920 | |||||
| For 2-resistor supervision: | |||||||
| State | LOW | HIGH | LOW | HIGH | LOW | HIGH | STATE |
| short | 0 | 2.34 | 2.5 | 2.89 | 0 | 1.26 | 3 |
| closed | 2.03 | 3.12 | 2.89 | 3.59 | 1.26 | 2.94 | 1 |
| open | 2.81 | 3.90 | 3.59 | 4.35 | 2.94 | 4.19 | 0 |
| cut | 3.59 | 5.00 | 4.35 | 5.00 | 4.19 | 5.00 | 2 |
| For 1-resistor supervision: | |||||||
| State | LOW | HIGH | LOW | HIGH | LOW | HIGH | STATE |
| closed | 0 | 2.34 | 2.50 | 2.94 | 0 | 1.27 | 1 |
| open | 2.03 | 3.12 | 2.94 | 4.15 | 1.27 | 3.75 | 0 |
| cut | 2.81 | 5.00 | 4.15 | 5.00 | 3.75 | 5.00 | 2 |
Table 1
As you can see, the voltage values for the first group (7716, 7718, 7756) overlap from one state to the next. In this case, the point will remain in the current state until its’ upper or lower limit is crossed, much the same as a temperature differential. The various installation guides for each of these DCU types differ as to what value of resistor and what length of wire can be used; but, if the end result of the circuit produces these voltages, the supervised DI/DA will work. Therefore, you can vary the resistor values and/or wire length but these voltage levels must still be achieved.
Don’t let the order in which the state descriptions appear in Table 1 mislead you. The order you see in the table is not the order in which the system expects to find them. They should be entered as OPEN-CLSD-CUT-SHRT (in that order) in the State Description editor for a 2-resistor DI/DA point and OPEN-CLSD-CUT for a 1-resistor DI/DA point. For check out purposes, the STATE number can be viewed from the Hand Held Console when displaying the DI/DA point. The state values are 0-3, which are found in the last column of Table 1.
Another useful technique for displaying these voltage values within I/NET 7700 is to temporarily assign the input as an AI. The conversion coefficient can be determined using the I/NET 7700 calculator (see Figure 1.). The Equipment counts high is 4095 for the 7716PCU, 7718PCU, and the upper board inputs of the 7756PCU; 32,767 for the lower board on the 7756PCU; and 255 for the 7910, 20,30, and 40. Engineering units low and high are 0 and 5 respectively for all controllers. The value of the point can now be viewed from the screen or the Hand Held Console.
05/23/95 14:21:31 Tue Conversion coefficients Host 00 (shm) Link 01 [020 link] DCU 02 [PCU 7716] Select (Linear Flow) # M B --+------------+------------ 0 0.001221 0 Conversion equation Linear 1 0 0 2 0 0 Equipment counts low 0 3 0 0 Equipment counts high 4095 4 0 0 Engineering units low 0 5 0 0 Engineering units high 5 6 0 0 7 0 0 8 0 0 9 0 0 10 0 0 11 0 0 12 0 0 13 0 0 14 0 0 15 0 0 Press ESC to copy to M & B
Figure 1
Keep in mind that the 7718PCU is switchable for the pull up voltage to either 5 or 15 VDC. For the supervised DI/DA points to work properly, jumper J38 must be set to 5V.
A simpler approach to ensure a DI/DA supervised point will work correctly is to limit the length of the wire and thus the resistance that the wire adds to the circuit. If you use 1% 1000 ohm resistors(as recommended), the maximum total resistance that your wire can add for the supervised point to work properly is listed below.
| DCU Type | 1-resistor configuration | 2-resistor configuration |
| 7716, 18, 56 | 650 ohms | 1250 ohms |
| 7910, 30, 40 | 300 ohms | 400 ohms |
| 7920 | 325 ohms | 325 ohms |
Table 2
Note: The value for 1 resistor configuration should be within +/-10 ohms and 2 resistor configuration should be within +/-20 ohms to account for resistor tolerances.
These values include both conductors of the wire (shorted together at one end and measured from conductor to conductor at the other end). They allow for (in the case of 2-resistor supervision) the short to be detected at any point on the wire (all the way out to the contact). These are the maximum resistance values and the actual resistance should be kept as low as possible. These values were calculated using the voltages in Table 1 and assume that the supervision resistors are exactly 1k ohms. The values for the first group take into account the overlap of voltage levels between states and are intended to avoid those zones.
These values might lead one to believe that a supervised DI/DA point can be wired with ten or twenty-thousand feet of wire. This is not the case due to the noise which wire can pick up and make the input unstable. So the distance should be kept as short as possible.
