Diablo Controls DSP-20-LV-R Dual Channel Loop Detector Technical Details
The Diablo Controls DSP-20-LV-R is a dual-channel inductive vehicle loop detector designed for automatic gates, parking controls, access-control entrances, and other applications that require two roadway loop inputs. The detector can operate the two loops as independent channels or combine them through built-in directional logic to provide an output based on a vehicle's direction of travel.
Diablo Controls now identifies the normally open low-voltage version as DSP-20-NO-LV and specifically notes that it was previously known as DSP-20-LV-R. This part-number change is important when replacing an older detector or comparing current distributor inventory.
Legacy DSP-20-LV-R and Current DSP-20-NO-LV
The DSP-20-LV-R is a legacy product designation still found in existing gate and parking installations. Diablo's current application documentation identifies the equivalent current configuration as DSP-20-NO-LV.
- DSP-20-LV-R: Previous product designation.
- DSP-20-NO-LV: Current normally open low-voltage relay designation.
- DSP-20-NC-LV: Normally closed relay version.
- DSP-20-SS-LV: Solid-state output version.
Do not substitute the NC or solid-state version solely because the enclosure and 11-pin connection look similar. The output behavior and electrical interface are different.
Two Independent Channels or Directional Logic
The DSP-20 can function as two independent single-loop detector channels. Each channel can provide its own vehicle-detection output and can be individually configured for Presence or Pulse operation.
The detector can also operate in Directional Logic mode. In that mode, two loops are installed in the same travel lane. The detector monitors which loop is occupied first and then waits for the vehicle to reach the second loop while the first remains occupied. The resulting output can be used by compatible parking and access equipment to respond differently based on direction of travel.
Advanced Dual-Channel Scanning
Rather than operating two completely independent loop oscillators continuously, the DSP-20 uses channel-scanning technology. Diablo designed this system to improve electrical noise tolerance and reduce interaction between Channel 1 and Channel 2.
This can allow the two roadway loops to be installed closer together, including some applications where the loop areas overlap. Proper loop design, frequency selection, and installation practices are still required.
Features and Specifications
| Specification | Details |
| Brand | Diablo Controls |
| Legacy Part Number | DSP-20-LV-R |
| Current Equivalent Designation | DSP-20-NO-LV |
| Product Type | Dual-channel inductive vehicle loop detector |
| Loop Channels | 2 |
| Operating Modes | Two independent channels or Directional Logic |
| Relay-Version Power | 10.5 to 35VDC or 9 to 28VAC |
| Typical Operating Current | Approximately 25 mA |
| Maximum Relay-Version Current | 120 mA with both relays energized |
| Connector | 11-pin relay socket |
| Outputs | 2 normally open relay outputs on DSP-20-LV-R / current DSP-20-NO-LV configuration |
| Relay Rating | 1A at 125V |
| Loop Inductance Range | 20 to 1500 microHenries including lead-in inductance |
| Sensitivity Levels | 4 independently selectable per channel |
| Frequency Settings | 2 per channel |
| Sensitivity Boost | Selectable for both channels |
| Presence Modes | Normal Presence or Extended Presence |
| Normal Presence Example | Approximately 1 hour at 1 percent delta L/L vehicle detection |
| Extended Presence Example | Approximately 18 hours at 1 percent delta L/L vehicle detection |
| Pulse Type | Pulse On Entry |
| Pulse Duration | Approximately 150 ms followed by 150 ms off period |
| Response Time | Approximately 150 ms +/- 25 ms |
| Presence Failure Mode | Selectable Fail-Safe or Fail-Secure |
| Pulse Failure Mode | Fail-Secure |
| Operating Temperature | -35 F to 165 F |
| Housing Size | Approximately 2.36 in H x 1.75 in W x 4.09 in D |
Four Sensitivity Levels Per Channel
| Sensitivity | Approximate Delta L/L |
| Low | 0.50 percent |
| Medium Low | 0.10 percent |
| Medium High | 0.05 percent |
| High | 0.02 percent |
Each channel can be adjusted independently. Medium Low or Medium High is normally a better starting point than automatically selecting maximum sensitivity. Excessive sensitivity can increase unwanted detection from nearby moving metal, unstable loops, or electrical interference.
Sensitivity Boost for High-Bed Vehicles
Sensitivity Boost increases sensitivity after the detector has already established a vehicle call. This is useful when a truck or trailer initially produces a strong detection but the high-bed center section produces a weaker inductive signature as it passes across the loop.
Proper loop dimensions are still important. Sensitivity Boost should not be used to compensate for a poorly sized or damaged roadway loop.
Normal and Extended Presence
The DSP-20 does not provide true infinite presence. In Normal Presence mode, the detector slowly retunes after a vehicle remains continuously over the loop for several minutes. Diablo gives approximately one hour as a typical hold example for a 1 percent delta L/L vehicle.
Extended Presence increases that example hold time to approximately 18 hours. Actual hold time depends on loop construction, vehicle position, signal strength, environmental conditions, and other installation factors.
Pulse On Entry and Flicker Display
Each channel can be configured for Pulse On Entry instead of Presence. When a vehicle is first detected, the channel produces an approximately 150 ms pulse. It will not issue another vehicle-entry pulse until the applicable loop becomes vacant.
After the output pulse has ended, Diablo's Flicker display allows the red channel LED to continue showing that the roadway loop is still occupied. This helps a technician distinguish between a normal occupied loop and a channel that has stopped functioning.
Fail-Safe and Fail-Secure Operation
For channels operating in Presence mode, the DSP-20 can be configured for Fail-Safe or Fail-Secure operation.
- Fail-Safe: The output stays activated when the detector identifies a loop failure.
- Fail-Secure: The output remains deactivated during the loop failure.
The selected fail behavior applies to both channels at the same time. Pulse mode is always Fail-Secure.
The correct failure configuration depends on the purpose of the connected controller input. Follow the gate, parking, or access-control manufacturer's requirements rather than changing the failure mode without confirming the application.
Loop Fault Monitoring and Memory
The DSP-20 continuously monitors both loop circuits. Separate red Channel 1 and Channel 2 LEDs can indicate normal vehicle occupancy, pulse operation, active loop faults, and prior recovered loop faults.
This is useful when troubleshooting intermittent problems. A roadway loop may open or short temporarily because of pavement movement, moisture, a failing splice, or damaged lead-in wiring and then return to normal before a technician arrives. Fault memory can indicate that such a problem occurred.
DSP-20-LV-R 11-Pin Wiring Reference
The former DSP-20-LV-R corresponds to the current normally open relay configuration. Current DSP-20-NO-LV pin assignments are:
| Pin | Function |
| 1 | Power / DC Positive |
| 2 | Neutral / DC Negative |
| 3 | Channel 2 Relay Common |
| 4 | Earth Ground |
| 5 | Channel 1 Relay Common |
| 6 | Channel 1 Normally Open Output |
| 7 | Channel 1 Loop |
| 8 | Channel 1 Loop |
| 9 | Channel 2 Loop |
| 10 | Channel 2 Loop |
| 11 | Channel 2 Normally Open Output |
Important Relay Output Warning
The DSP-20-LV-R / DSP-20-NO-LV configuration does not provide two complete Form C relay contact sets. Each channel has a relay Common and Normally Open output.
If the existing installation requires normally closed contacts, verify the DSP-20-NC-LV instead. If the controller requires electronic outputs, verify the DSP-20-SS-LV. Do not substitute these versions without checking the connected equipment.
DSP-20-LV-R vs. Other DSP-20 Versions
- DSP-20-LV-R / DSP-20-NO-LV: Low-voltage normally open relay version.
- DSP-20-NC-LV: Low-voltage normally closed relay version.
- DSP-20-SS-LV: Low-voltage optically isolated solid-state output version.
The relay and solid-state versions also have different minimum operating-voltage specifications. Verify the suffix and controller requirements before replacing an existing detector.
Typical Applications
- Automatic gate dual-loop vehicle detection
- Parking entrance and exit control
- Vehicle direction detection
- Access-control entrances
- Two independent roadway detection zones
- Pulse-based parking or access inputs
- Presence-based vehicle-control inputs when approved by the controller manufacturer
Package Contents
The DSP-20-LV-R should be treated as the detector module only unless the seller specifically states that an 11-pin socket or wiring harness is included. Roadway loops, loop wire, detector socket, gate operator, access controller, enclosure, and other installation materials should not be assumed included.
Before Ordering Checklist
- Confirm the existing part number is DSP-20-LV-R.
- For current production, verify whether DSP-20-NO-LV is the required replacement designation.
- Confirm that normally open relay outputs are required.
- Do not substitute DSP-20-NC-LV or DSP-20-SS-LV without checking the controller.
- Verify the 11-pin socket and pin assignments.
- Confirm the available supply is within 10.5 to 35VDC or 9 to 28VAC for the relay version.
- Verify both roadway loops fall within the supported detector range and are electrically sound.
- Determine whether the two channels will operate independently or in Directional Logic mode.
- Determine whether each channel requires Presence or Pulse operation.
- Confirm whether Normal or Extended Presence is appropriate.
- Verify the required Fail-Safe or Fail-Secure behavior for the assigned controller inputs.
Technician Note
If one channel works normally while the second channel reports faults, do not automatically replace the DSP-20. Swap or independently test the roadway loop circuits according to proper service procedures to determine whether the fault follows the loop or detector channel.
If both loops detect vehicles correctly in independent mode but Directional Logic does not behave as expected, verify loop order, vehicle travel direction, spacing between the two loops, and the Directional Logic switch setting before replacing the detector.
Installation and Safety Notes
Connect each detector output only to the gate, parking, or access-control input intended by the equipment manufacturer. Do not change Fail-Safe, Fail-Secure, Presence, or Pulse settings without understanding how the controller uses that input.
An inductive vehicle loop detector does not replace required monitored photo eyes, safety edges, emergency access devices, fire-access equipment, or other gate entrapment-protection systems. Never bypass required safety circuits to make a loop detector input operate.
Product Questions and Answers
Is Diablo DSP-20-LV-R still the current part number?
Diablo's current detector application guide identifies DSP-20-NO-LV as the normally open low-voltage version and states that it was previously known as DSP-20-LV-R. Verify DSP-20-NO-LV when ordering a current replacement.
How many roadway loops can the DSP-20-LV-R monitor?
The DSP-20 is a dual-channel detector and monitors two separate inductive loop circuits. The channels can operate independently or together in Directional Logic mode.
What voltage does the DSP-20-LV-R relay version require?
Current Diablo technical data specifies 10.5 to 35VDC or 9 to 28VAC for the relay-output DSP-20 versions. Verify the existing controller supply before replacing an older detector.
Does the DSP-20-LV-R have two Form C relay outputs?
No. The current normally open equivalent provides a Common and Normally Open contact for each channel. If normally closed outputs are required, verify the separate DSP-20-NC-LV version.
Can the two DSP-20 channels determine vehicle direction?
Yes. In Directional Logic mode, the detector evaluates the order in which the two roadway loops are occupied and can activate the corresponding output based on the vehicle's direction of travel.
Does the DSP-20 provide infinite vehicle presence?
No. Normal Presence typically holds a representative vehicle for about one hour, while Extended Presence can increase that example to about 18 hours. Actual hold time depends on the loop and vehicle signal.
What should I check if one DSP-20 channel shows a loop fault?
Inspect the affected roadway loop, lead-in cable, splices, and terminal connections for an open, short, moisture problem, or intermittent wiring condition. The DSP-20 also stores indication of recovered faults, so a loop problem may have occurred even if the circuit is currently operating.
Can the DSP-20 vehicle loops replace gate photo eyes or safety edges?
No. The DSP-20 provides vehicle detection and directional logic. Required monitored photo eyes, safety edges, and other gate entrapment-protection devices must remain properly installed and operational.
