Bypassing the 1 W Alarm‑Enable Threshold on the 3141 Channel Power Monitor

Purpose

The 3141 CPM suppresses all alarms whenever it senses less than 1 W of forward power unless the PTT (Push‑To‑Talk) is enabled and input indicates the transmitter is keyed. In low‑power test setups or maintenance windows this gating can mask genuine faults. The procedure below shows how to use an un‑wired PTT input to keep the alarms active at any power level.

Principle of the Work‑around

• PTT logic options
  • Open (Normally Open) – Idle = open circuit, Keyed = closed circuit.
  • Closed (Normally Closed) – Idle = closed circuit, Keyed = open circuit.
• When you select Closed but leave the PTT terminals open / floating, the 3141 interprets the line as continuously keyed. This bypasses the >1 W gating requirement, so all alarm thresholds are evaluated even below 1 W.

⚠️ Caution: This method intentionally defeats the built‑in gating. Verify that nuisance alarms will not disrupt site operations before enabling it.

Step‑by‑Step Instructions

1. Log in to the 3141 web interface and click Settings on the top menu bar.
2. In the left‑hand pane, choose Digital Sensors.
3. Locate each 4043 / 4042 sensor row that needs low‑power alarming and:
   • In the PTT Normally column, select Closed from the drop‑down list.
   • Leave the physical PTT terminals on the rear panel unwired.
4. Click Save Settings (lower left).
5. Return to Table View and confirm that alarms now trigger as expected even when forward power is < 1 W.

Reverting to Normal Operation

When a true PTT signal becomes available:

1. Wire the dry‑contact or logic output from the transmitter to the CPM’s PTT terminals.
2. Set PTT Normally to the polarity that matches the transmitter (usually Open).
3. Re‑validate alarm thresholds.