Sea-Bird CTD - Electronic faults and wiring errors

Electronic faults

The original guide distinguishes several cases of electronic faults or damage caused by handling errors.

Loss of the Digiquartz pressure-sensor signal

This problem was encountered after transport or after the CTD was set down too roughly on deck. In the cases described, the wires from the internal Digiquartz pressure sensor were cut at their arrival on the bottom end cap wiring board.

Power connector wiring errors

The guide cites several particularly destructive wiring errors:

1. sea-cable power connected to the bottom contact socket
2. power connected to a socket dedicated to a pump

In the first case, the Modulo 12P board can be damaged, along with other boards or components in line with the power supply. It is therefore recommended to print the TAP location diagrams in advance before any reconnection on board.

The 250 V DC will destroy circuit U3 (CD4021 shift register), as well as circuit U4 (CD4040 12-bit counter) on the Modulo 12P board.

According to the manufacturer Sea-Bird, when the Sea-cable is connected for more than 30 s to the bottom contact, it can also damage the Logic1 board and the AP counter board dedicated to pressure measurement (U7 circuit failed). It should be noted that the five AP counter boards used for frequency measurements are interchangeable.

If a new Modulo 12P board is installed, the measurement-chain calibration of the AD590 sensor used for temperature compensation of the Digiquartz pressure sensor must be redone (12-bit A/D converter U5 and op-amp U6) to recalculate the M and B coefficients. Two points are enough to determine the slope of the measurement circuit. It is strongly recommended to determine these coefficients beforehand when the replacement board is received.

Since 2007, Sea-Bird has replaced the JB6 (RMG-2FS) bottom contact connector of the SBE9+ fish with a VSG-2BCL connector and replaced the RMG-2FS cable with a VMG-2FS.

In the second case, Sea-cable power connected to the socket dedicated to a pump results in a global system error. The Modulo 12P board of the SBE9+ CTD is damaged: Zener D2, capacitor C20, and circuit U7 must be replaced. According to Sea-Bird, the transmit card can also be damaged by this type of wiring error, especially the components in line with the pump power supply: C8, R8, and Q5 on the SBE9+ transmit card.

On recent CTDs, connector locations are marked on the TAPs. It is nevertheless recommended to print the TAP location diagrams and keep them in view before attempting any new connection on board.

Major short circuit on the power cable

A major short circuit on the power cable can burn several circuits (U5, U6, U9) on the Modulo 12P board.

Repeated display of 0000, 1111, 2222… series

The guide links this symptom to a problem on the +5V or +/-12V power supply of the SBE11+ deck unit.

Transient pump start

A very brief pump start followed by an immediate stop can point to the Transmitter and pump delay board or to the U6A circuit of type CD4013.

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