SHERLOCK 804 Refrigerant Gas Monitoring System

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Monitoring Panel

The Sherlock 804 Control Module is a hardwired, electronic control panel that is capable of monitoring the analog output signal of up to eight Sherlock Refrigerant Gas Sensor or Sherlock Oxygen Depletion Sensors and four digital dry-contact switches. The Control Module can activate eight, Form C SPDT relay contacts based upon the programmed alarm level setpoint levels of each sensor. The Control Module can be located in the area to be monitored, or in a separate location, typically outside of the monitored room.

Monitoring Points

Each monitoring point consists of an analog signal generating sensor connected to the control module via discrete, three conductor cable. Each sensor can be mounted up to 800 feet away in locations where leaked refrigerant is likely to concentrate.

The gas sensors are available in four varieties:

Ceramic Metal Oxide Semiconductor (CMOS) or Solid State Sensor

Non-Dispursive, Pyro-Electric Infrared Sensor.

Oxygen Depletion Electro-chemical Sensor.

Electrochemical Sensor

Alarm Level Settings

The Sherlock 804 allows you to set three unique Alarm Setpoints for each individual sensor throughout their operating. When an Alarm Setpoint is exceeded, a corresponding set of alarm relays are activated Each Alarm Setpoint has a programable Alarm Delay, 1 to 120 minutes. Sensor readings are required to exceed an Alarm Setpoint for the programmed amount of time before the control activates the corresponding alarm relay contacts. For example, if the Alarm Setpoint is 200 and the Alarm Delay is five minutes, the control will enter an alarm condition only if the sensor detects a level of 200 or higher for more than five minutes.

Alarm level #1 and Alarm Level #2 on every sensor has the option of using the Time Weighted Average (TWA) reading as the input reading. Time Weighted Average reading of a sensor is the average reading of a sensor input over a period of time.

Alarm Indication

All alarms are logged to indicate which sensor went in and out of any of the three alarm levels, the time and date of the alarm. The alarm log stores the last 32 alarms. When a sensor is in alarm, an LED on the front panel will turn to red color, the on-board beeper will be beeping and the display will go into "IN ALARM" screen every five seconds. The individual sensor causing the alarm also displays the "ALARM" message.

Alarm Relay Contacts

The Sherlock 804 provides two fused SPDT (Single Pole Double Throw) relay outputs for each alarm level that switch positions in the event of an alarm condition. The 'B' relay for each alarm level can be temporarily or permanently silenced by pushing the respective alarm silence button on the front panel. The relay will re-activate after a programmed period of time, if the alarm condition is not cleared. The 'A' relay however will remain active until the alarm condition is cleared. The Sherlock 804 can be programmed so that the alarm is cleared automatically when the air is cleared below the alarm setpoint (UNLATCHED) It can also be programmed so the alarm is latched "ON" until the alarm is manually reset. Each alarm level can be configured so the relays are "Energized to Alarm" (where the C-NC contacts open on alarm) or "De-Energized to Alarm" (where the relay is energized during normal operations and the C-NC contacts close on alarm).

Analog Signal Generator (Optional)

Sherlock 804 has an optional 0-5 V / 0-10 V / 4-20 mA analog output for each sensor. Either of these signals can be incorporated to any commercially used monitoring and alarming system or in-house Data Management System.

Zone Isolation Alarm Relays (Optional)

An optional Zone Isolation Relay Kit is available for the Sherlock 804.  This kit allows the user to directly control or activated alarm circuitry specific to each sensor.  This circuitry can include Audio / Visual alarm appliances mounted within the location where each sensor is located.  The relays can be used to shutdown refrigeration or mechanical equipment within room where each sensor is located.

Systems Fault Monitoring

The Sherlock 804 constantly monitors the wiring to the sensors. Should any of the activated sensor wires be cut or disconnected, "OPEN" will appear on the SHERLOCK display, the alarm #1 and system alarm are activated and the condition is logged. In addition to the three alarm levels the Sherlock 804 is also equipped with a SYSTEM FAULT ALARM. This alarm is triggered when the system malfunctions (i.e. The sensor wire is cut or inter-connect cable is cut).

Setback Alarm Settings

In some locations the sensor may be expected to function in two different environments. For example, the sensor may have to perform in still air (i.e. with the exhaust fan off) and in moving air ( i.e. with the exhaust fan on), or the sensor may be used in a location where changes in air quality, perhaps caused by the use of propane powered floor buffers, elevates the sensor readings. The SHERLOCK 804 provides a feature called SETBACK to accommodate alternate environments under which the sensor would operate. SETBACK provides a second ALARM SETPOINT and a second ALARM DELAY enabling the sensor to perform in this second environment. The SHERLOCK 804 switches to the second set of parameters when a dry contact (i.e. air flow, sail switch or timer) closes or on a daily time schedule.

Each sensor can be programmed with one of five SETBACK options:


2) SETBACK triggered by setback input 1 only

3) SETBACK triggered by setback input 2 only

4) SETBACK triggered by setback input 1 or the setback time clock

5) SETBACK triggered by the setback time clock only

Each sensor can be programmed with only one SETBACK option; however, different sensors may be programmed to follow different options.