Principles of Operation:
Analog Inputs

Analog Inputs are available for Aquadopp Current Meters, Aquadopp Current Profilers, Vector Velocimeters, AWACs and Continentals. This page describes how you use the analog inputs and provides specifications for the analog inputs.

To use analog inputs:

Your instrument must have the correct internal wiring harness installed. Most instruments come with an 8-pin connector.  Optionally on some products, you may specify a 2-connector end-cap with a dedicated 5-pin connector for analog sensors.   Different wiring harnesses support analog input, analog output, RS422, SDI-12, synchronizations, etc. If you have an Aquadopp (Current Meter or Profiler) or a Vector, then the chances are good that the harness supports analog inputs. Wiring harnesses are inexpensive and can be purchased from Nortek AS or NortekUSA.

Figure 1. Analog input circuit. The op amp has effectively infinite input impedence.

Powering external sensors  

Instruments with analog inputs can also supply power to external sensors. The following outlines how external power works:

• Power outputs can use 5 VDC, 12 VDC or direct battery voltage. This choice must be made at the time of purchase, and it is hard-wired on the circuit board.
• Power at 5 and 12 VDC comes through switching regulators. This means that power drawn from the battery pack is 15-18% greater than the power consumed by the external device.
• The output voltage is protected against short-circuit with a 1-amp fuse.
• The output voltage turns on at least 0.8 s before the beginning of a measurement interval, and it turns off again at the end. The first measurement of the analog inputs occurs roughly 0.9 s after power is applied.
• The planning software does not consider power consumption of your external devices when it plans deployments.

Data sampling  

For all instruments (except for the Vector Velocimeter), the analog inputs are sampled once near the beginning of each second during the measurement interval, and the instrument computes and records the average over the measurement interval.

The Vector Velocimeter provides two choices for sampling the analog signals:

1. SLOW -- when "slow" is selected, the Vector will sample the analog channels every 1 sec during the velocity measurements (as described above), regardless of the configured velocity sample rate.
2. FAST -- when "fast" is selected, the Vector will sample the analog channels at the same rate as the velocity measurements are configured (up to 64 Hz) with no averaging.