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Microlink Measurement and Control Systems

Microlink 3000: Modular Measurement and Control


Microlink 307x - High Speed Modules

The 3070 module allows high speed scanning by multiplexing signals from one or more analogue input modules. A a separate multiplexer is therefore not required. The 3070 module is held in a Microlink frame, along with analogue-to-digital converter and analogue input modules.

You would use a 3070 module when:

The limit of the data transfer rate depends on several factors including the type of communications (Ethernet, GPIB or serial) and the analogue-to-digital converter chosen. For example, with a Microlink 3042 A-D module, you are limited to 40 000 samples per second over GPIB. (For higher speeds consider the Microlink 770 USB unit.)

The Windmill Streamer software is especially suitable for 3070 systems, as it streams data to disk at maximum speeds. The Microlink 3000 configuration when using Streamer software is:


Microlink 3070 - High Speed Scanning Module

The Microlink 3070 allows high speed digitisation of analogue signals. You use it in conjunction with a 304x A-D converter and one or more analogue input modules (305x or 306x). These other modules can be used in their normal slow mode even when the 3070 is present in the Microlink frame.

How the 3070 Scans Analogue Inputs

Microlink 3000 multiplexes analogue inputs, at speed, in a very flexible way. There are several factors to consider when building such a flexible multiplexing system, described below.

Multiplexing Analogue inputs
Any number of analogue input channels can be scanned at high speed. The channels to be included in the scan are selected through software, along with the gain range and other configuration details for individual inputs. When scanning starts the system goes to the leftmost analogue input module and takes the first sample from the first channel in the scan. The scan goes from left to right in module order. The 3070 maintains a count of channels scanned and returns to the first channel after the required readings have been taken.

The time taken from the first sample of the first channel to the next sample of the first channel is known as the scan rate. The time between sampling the first channel and sampling the second channel is the inter-channel rate.

Setting the Scan and Inter-Channel Rates
Experience has shown that their is a need for flexibility in how channels are sampled. Signals may be changing on widely different time scales. For example, the pressure inside an engine cylinder varies much faster than the temperature of the engine's cooling system, yet you may need to record both signals.

To cope with situations like these, the 3070 allows for two groups of inputs - A and B. These two groups may be used to specify dual scan rates so that one group of signals (A) can be sampled in every scan, while signals in group B are samples every nth scan. Alternatively the two groups may be used to specify dual settling times. Here group A might be thermocouples, where long leads necessitate the use of a low-pass filter to remove noise from the signal, while group B might be good quality voltage signals with little noise. The inputs that are filtered will require a longer settling time than those which do not require filtering. So in dual settling time systems two different groups of channels have different inter-channel rates. This maximises the overall scan rate by not slowing down the channel switching where the longer settling time is not required.

Starting and Stopping the Scan
You can start and stop data acquisition by pressing a button in software (a software trigger) or from a logic pulse derived from some external event (an external trigger). In either case the computer will need to be ready to receive the stream of values that will be generated by the A-D converter. To provide for the software delays involved in moving from configuring the 3000 Series modules, to the state where the computer is ready to receive data, a programmable trigger pulse delay is available. This is typically 20 ms, and may be considered a delay before the system is armed.

The simplest way to stop the scan is for the software to collect as many data samples as are required. However, there are times when a more definite approach has benefits

A count of complete scans allows sampling to be stopped when the required amount have been digitised. Sampling restarts when the next trigger is received. This is particularly useful when the 3070 is used with buffered A-Ds, because the system can be left collecting short waveform sections following each trigger pulse, and the computer can process this data at convenient intervals.

Sampling can also be stopped on an external signal. This allows the trigger input signal to be used for gated data acquisition. When the trigger input is in the STOP state sampling cannot occur. When the trigger input leaves the STOP state sampling starts and continues until the trigger input returns to the STOP state. If the trigger input leaves the STOP state again, sampling restarts. This lets you synchronise capture from external instruments with their own internal scanning control.

Using an External Clock
The above discussion revolves around the 3070 producing, at programmable intervals, sample pulses which control the scan. By disabling the internal clock through software, the external clock input is activated. Now a scan is performed at each positive edge at the clock input.

Specifications

Sample timings are derived from a 4 MHz quartz crystal
Initial adjustment = ±2 ppm
Drift over temperature range 0-50oC = ±50 ppm
Scan rate = basic rate x multiplier
basic rate = 2 to 65535 in 0.25 µsec units
multiplier = 2 to 65535
Channel rate (A,B) = 2 to 65535 in 4 µsec units
Scan length A = 1 to 32767
Scan length B = 0 to 32767
Trigger pulse delay = 1 to 65335 x 100 µsec (nominal)
Trigger output pulse width = trigger pulse delay
All inputs and outputs are TTL 5 V CMOS, contact closure, compatible.
Trigger output is capable of driving 2 TTL loads.

Microlink 3071 - High Speed Digital Buffer

The Microlink 3071 module has a data buffer for 16 digital input lines. The buffer provides intermediate storage of readings prior to transfer to the computer. At each positive going edge of the input to the Latch Data input, the state of the 16 digital inputs are latched into the FIFO (first in first out) memory of the 3071. This means that the data lines can be latched by an external clock. The computer can read the buffer before or after a high speed scan without interfering with the collection in progress.

You can use several 3071 modules in the frame to latch digital lines in groups of 16. With the addition of a Microlink 3802 modules, you can latch and store a count of pulses at each clock input.


Software Support

You can control a Microlink 3070 system with Streamer software. Alternatively you can program the Microlink yourself: ask for our programming manuals and example programs.


Other Analogue Input Options

The Microlink 3000 system is the leading, modular, data acquisition and control system. However, it may be that your needs can be met at a lower cost by a unit which plugs into your PC's USB port. If this is the case see our USB overview. For higher speeds we have the Microlink 770 USB unit.


More Information

For more information about high speed data capture, please send for our free Systems Catalogue or download the Microlink 3070 Manual. You can also ask our advice on your project.


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Last revised April 2002
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