2.4.1 Pulse/Timer

Summary Description

Figure 2.4.1.0-A

The NEXSYS Pulse/Timer (PT1) is a Series C (8 Pin) dual-channel edge detector and pulse generator. Each channel is independent and provides stable retriggerable/resettable one-shot operation for fixed timing applications. The trigger inputs allow unlimited rise and fall transitions that can be specified to sense either a rising-edge (Low to High) or falling-edge (High to Low), see Figure 2.4.1.0-A. Input signal level (edge) definitions are provided in the Parametric Table, see Figure 2.4.1.1-A.

The PT1 can generate a wide range of timed pulse widths that are specified as either Active High (High-Z, Open) or Active Low (Ground). The specified time intervals range from 125 ms to 20 sec. Each channel includes a Low-triggered Reset Input (PINS 1, 7) for immediate deactivation of pulsed Outputs, Q1 and Q2 (PINS 8, 6). The channels can be wired in series to provide a propagation delay for a custom, time-delayed one-shot. The PT1 offers a solid-state replacement for electromechanical time delay relays. Other uses include reciprocal transition detection (i.e., “Weight On/Off Wheels”) and limit sensor applications.

The NEXSYS Pulse/Timer (PT1) is a commercial-off-the-shelf (COTS) item. This standard catalog hardware includes features to allow for flexible interface design solutions while also meeting aircraft performance standards. The PT is designed, tested, and qualified to MIL-PRF-22885/116, MIL-PRF-22885/117, DO-160 and MIL-STD-461 requirements. Specifications are available in our MIL-PRF and DO-160 Documents page, and the qualification table is available in Appendix A.

Input Characteristics

The NEXSYS Pulse/Timer inputs are Power (28V), Ground (GND), Trigger 1 (TR 1), Reset 1 (/RST 1), Trigger 2 (TR 2) and Reset 2 (/RST 2). The inputs include the following characteristics for edge detection and timed-output control. Pulse/Timer input circuity is diode isolated, buffered, and debounced for reliable operation. See additional sections for specific details concerning the Input/Output (I/O) interface.

28V (PIN 4): Operating Voltage (Nom.), Current Draw 4 mA (Max).
GND (PIN 5): Continuous Ground required, otherwise, inadvertent operation could occur.
TR 1 (PIN 3), TR 2 (PIN 2): Detect a rising () or falling () edge signal level transition, which functions as the control interface trigger to drive timed outputs.
/RST 1 (PIN 1), /RST 2 (PIN 7): Immediate termination (reset) of the pulsed output.

Output Characteristics

The NEXSYS Pulse/Timer features conditioned outputs Channel 1 (Q1) and Channel 2 (Q2) Q to perform functions that may originate from remote inputs or switch closures. All outputs are open-drain High-Z (Open) when not active, fused, and surge-protected against transients and overload conditions. The output load capacity is 2.0 A, see Figure 2.4.1.1-A (Operating Parameters) for electrical load rating types.

Q1 (PIN 8), Q2 (PIN 6): Independent outputs that are one-shot drivers, available in two options. Specified timing options for the output pulse range from 125 ms to 20 seconds.

Configuration Options

The NEXSYS Pulse/Timer offers numerous configurations for custom, solid-state edge-detection and pulsed-output control. The device powers-up in a specified, known state. After power-up, the TR 1 and TR 2 inputs detect signal transitions to control the Q1 and Q2 outputs.

Trigger Options TR 1 and TR 2 (PINS 3, 2), are independent and specified as either:

Positive: The rising-edge option is specified for detecting a rising level transition, away from Low (Ground).
Negative: The falling-edge option is specified for detecting a falling edge level transition, toward Low (Ground).

Pulse Length Options dual independent channels specified as either:

Channel 1, Channel 2: 125 ms, 250 ms, 500 ms, 1 sec, 2.5 sec, 5 sec, 10 sec, 20 sec.

Active Pulse Options Q1 and Q2 (PINS 8, 6), are independent and specified as either:

Active High: Normally Low (Ground) and pulses High-Z (Open) for the specified pulse length.
Active Low: Normally High-Z (Open) and pulses Low (Ground) for the specified pulse length.

Truth Table

For a description of the operational states and performance of the Pulse/Timer component, see Figure 2.4.1.0-B.

Figure 2.4.1.0-B

Input Selected Input Option Actual Input Received Output Response
Q1 or Q2
Active High-Z (Open) Normally Low (Ground)
Q1 or Q2
Active Low (Ground)
Normally High-Z (Open)
TR 1 OR TR 2 Rising (Positive)
Edge Detecting
Rising
(Positive)

Output transitions from Low (Ground) to High-Z (Open) for the specified pulse period Output transitions from High-Z (Open) to Low (Ground) for the specified pulse period
Falling (Negative)
No Change: Output remains at Low (Ground) No Change: Output remains at High-Z (Open)
Falling (Negative) Edge Detecting
Rising
(Positive)
No Change: Output remains at Low (Ground) No Change: Output remains at High-Z (Open)
Falling (Negative) Output transitions from Low (Ground) to High-Z (Open) for the specified pulse period Output transitions from High-Z (Open) to Low (Ground) for the specified pulse period
/RST 1 OR /RST 2 - Reset = High-Z (Open) Q1 and Q2 operate as defined above
- Reset = Low (Ground) Output is disabled (pulse cancelled) and is held at Low (Ground) Output is disabled (pulse cancelled) and is held High-Z (Open)

2.4.1.1 Pulse/Timer, Operating Parameters

Figure 2.4.1.1-A Parametric Table

Description Parameters
Operating Parameters
Operating Voltage (Max. / Nom. / Min.) +32 VDC / +28 VDC / +18 VDC
Power Supply Input Current 4 mA (Maximum)
Reset From Power Loss at 25°C 5 sec (Minimum) at +25°C
Hold Up On Power Loss at 25°C 200 ms (Minimum)
Input Parameters
/RST 1, /RST 2 at 25°C 55 ms (Minimum)
/TR 1, /TR 2 at 25°C 40 ms (Minimum)
* High Level Input Voltage ( VIH ) at 25°C +5 VDC (Minimum)
* Low Level Input Voltage ( VIL ) at 25°C +1.2 VDC (Maximum)
Low Level Input Current ( IIL ) at 25°C 1mA (Maximum)
Note: All signal inputs are diode isolated
Output Parameters
Output Load Capacity 2.0 A (Resistive) / 1.0 A (Motor) / 0.8 A (Inductive/Lamp)
On-State Resistance at 25°C Typical 0.07 ohms / Maximum 0.09 ohms
Off-State Resistance at 25°C Open Drain (High-Z), Fuse-Protected MOSFET,
+32 VDC Maximum
** Pulse Time Tolerance at 25°C +/- 10%
Temperature
Operating & Non-Operating -55° C to +85° C
Reliability
MIL-HDBK-217F, Notice 2
Airborne Inhabited Cargo (AIC)
at +40°C Continuous Operation
MTBF = 141,449 hrs

* VIL and VIH specifications are in reference to unit Ground.

** Time tolerance at EMC and environmental extremes is +/- 20%.

For Qualification Summary, see Appendix A