Microlink 3000: Modular Measurement and Control

Microlink 305x - Multi-Channel Analogue Input Modules

The Microlink 305x Series let you monitor analogue voltage, temperature, strain, resistance, pressure, current, etc. The Series consists of 6 modules. Your choice of module is held in a Microlink frame, along with an analogue-to-digital converter module.

All the 305x modules have differential inputs. You can use a differential input in single-ended mode by shorting one of the signal wires (usually the - input) directly to ground.

High Speed Sampling
Should you require a sample rate greater than a few tens of samples per second, you need a 3070 module as well as your 305x module. The Microlink 3070, when enabled, controls the sampling rate with crystal derived accuracy and allows the channels to be multiplexed at rates up to the throughput limit of the A-D converter module. When used with the 3070 the gain and offset of each individual channel in the 305x are set from software before sampling begins. Only those inputs needed are multiplexed, thus maximising sample rates.

Temperature, Pressure and Strain Monitoring
When using thermocouples choose a 3050 together with a 3902. The 3902 includes a cold junction sensing RTD with an associated constant current source. The cold junction is automatically connected to an auxiliary channel. Alternatively you can use a Microlink 3903 isothermal box. For resistance measurement, such as from RTDs or thermistors, choose the 3051.

If you are connecting balanced bridges such as pressure transducers, a 3050 with the 3904 Bridge Input module is appropriate. For strain gauge measurements use the 3052 module, half and quarter bridge termination resistors can be mounted on a 3904, which has been specially designed to provide excitation voltage distribution.

Microlink 3050 - 16 Voltage Inputs

The Microlink 3050 provides 16 differential analogue inputs (or 32 single-ended inputs). Use it in conjunction with an A-D converter, such as the 3042 module. High speed data capture, up to 40 000 samples per second, is available with the addition of a 3070 module. With the addition of the 3902 screw terminal module or a 3903 isothermal box, you can use the 3050 to monitor thermocouples. You can also use the 3050 to monitor balanced bridges like pressure transducers. For these you need to add a 3904 bridge input module.

The inputs are multiplexed, one being selected from software and passed to a programmable gain instrumentation amplifier. The module has 20 input ranges, which you select from software for each channel. The smallest range is 0 to 0.01 V, and the largest ±10 V.

You can choose which 304x A-D module you want to use with the 3050 module. If you only require slow sampling, use a 3044. This is because by integrating over a period of 20 msec it acts as a low pass filter. For faster sampling the 3042 is the most popular choice.

The 3050 itself has a low pass filter which you can turn on in software to limit the frequency response to 500 Hz. The settling time to 0.02% will then be 3.3 msec. The inputs of the 3050 can be isolated using the Microlink 3803 module.

Input Multiplexer
  On resistance                       ~400 Ohm
  Switch off leakage                  <2 nA
  Analogue voltage range              +11, -15 V
  Max safe input voltage:
    Power supply on                   ±35 V
    Power supply off                  ±20 V
  Break before make delay             1 usec
  Crosstalk                           75 dB
  Input impedance                     100 MOhm
  Offset voltage drift (gain=100)     1 uV/oC
  Input bias current                  ±30 nA
  Common mode rejection (gain=1000)   105 dB
  Common mode range                   ±10 V
  Frequency response                  50 kHz
  Settling time to 0.01%              15 usec
  Relative accuracy of gain ranges    0.02%
  Initial accuracy of gain and offset ±1 LSB
  Input noise voltage                 2 uV rms

Microlink 3051 - 16 Inputs with Resistance Option for RTDs and Thermistors

The 3051 module is essentially a 3050 with additional features to permit the measurement of resistance rather than voltage. You can therefore use it to measure temperatures using resistance temperature devices (RTDs or Pt100) or thermistors. Other variable resistance transducers can also be monitored. Strain gauges, though, are more conveniently handled with the 3052.

The module accepts up to 16 resistance devices in 2, 3 or 4 wire form. Each channel has + and - inputs to measure voltage across the resistors, plus a current source and compensation amplifier. You can choose whether to use the resistance option; if you don't use it the 3051 will measure voltages just like the 3050.

The current source can be 10, 100 or 1000 uA and you use software to make the selection. Using the 1 uA current source, a Pt100 will give a voltage reading of 100 mV at 0oC. The software will present all readings in the engineering units of your choice, oC or 0oF for example.

Specifications as 3050 plus
Current sources      10, 100, 1000 uA
Accuracy 10, 100 uA  0.2%
         1000 uA     0.02%

Microlink 3052 - 16 Inputs with Bridge Option for Strain

The 3052 enables strain gauge measurements to be placed under computer control. Sixteen strain gauge bridges can be monitored by any one module. These can be full, half or quarter bridge configuration. The module provides programmable gain and balance.

The module has the facility to measure the excitation voltage actually applied to the bridge. As this measurement can be carried out any time under software control, the strain gauge results can be adjusted for changes in the excitation voltage. The module can also produce a balancing voltage through a digital-to-analogue converter. The balance control is capable of balancing bridges producing output voltages that are up to 10% of their actual excitation voltage. There are three advantages of using a programmable offset to balance the bridge.

  1. The initial unstrained bridge output is often much larger than the strain signal to be measured. If it is not balanced out, it restricts the gain which can be applied to the signal and so restricts the signal resolution that can be obtained. Units not equipped with balance controls require the use of slow, high resolution, digital voltmeters.
  2. The computer can automatically balance the unstrained bridges.
  3. The computer can remember the balance setting required for all the bridges.

Like the 3050 module, the 3052 features 20 programmable ranges. The minimum change in signal that can be resolved with a 12-bit converter is 2.5 uV and is achieved by programming the gain to its highest level of x1000 (ie by selecting the ±0.01 or 0-0.01 V range from software). This will produce jitter in the converter readings from noise, so if only slow sampling is required use a Microlink 3044 or 3045 module instead. This is because by integrating over a period of 20 msec it acts as a low pass filter.

We also offer a module to provide excitation voltage distribution for the strain measurement (the excitation voltage must be supplied externally to the Microlink frame). The Microlink 3904 module gives 4 sets of 16 screw terminals to give excitation and signal connections for each of 16 bridges.

High Speed Sampling
Using the Microlink 3042 A-D module and the 3070 high speed module, you can sample strain gauge up to 40 000 times a second. Multiple 3052 modules are sampled at proportionally lower speeds. The 3052 module has RAM storage of gain and balance voltage so that these can be switched to each bridge at high speed during the scan.

Specifications as 3050 plus
Max balance range   10% bridge imbalance

Microlink 3053 - 16 Inputs with RMS Option

The 3053 module is basically a 3050 with a root mean square converter. When the input signal is received it is amplified and then converted to its rms equivalent. The reading will therefore always be a positive voltage. Since rms is a time averaged value, a significant time must elapse before the selection of a channel and the correct rms value being available. For the 3053 this settling time is 200 rms. When monitoring essentially 50 Hz signals the 3044 or 3045 integrating converter is recommended since it removes residual 50 Hz ripple. You can use software to disable the rms option, allowing you to use the 3053 exactly like a 3050.

For high speed scanning using rms, we offer the Microlink 3060.

Specifications as 3050 plus
Accuracy for 50 Hz signal             ±0.5%      
Settling time for channel switching   200 msec

Microlink 3054 - 32 Differential Voltage Inputs

Similar to a 3050, the Microlink 3054 provides 32 differential analogue inputs. It is used in conjunction with an analogue-to-digital converter, such as a Microlink 3042 module. High speed data capture is available with the addition of a Microlink 3070 module. Adding a 3902 or 3903 module lets you monitor 16 thermocouples.

Specifications as 3050 plus
Number of channels    32

Microlink 3055 - Relay Multiplexer

The Microlink 3055 has 16 low thermal EMF relay multiplexers, and a cold junction reference temperature circuit. It is appropriate for handling low voltage signals such as those from thermocouples, and can resolve temperatures to within ±0.025 oC. The thermal offset of the relays is better than 1 uV and they have a switching time of approximately 1 msec. The relays are accessed from screw terminals, which give 16 pairs of + and - inputs and 4 earth pins.

Specifications as 3050 plus
Relay thermal offset  1 uV
Relay switching time  1 msec
Charting analogue data

Software Support

You can control the Microlink 3000 with Windmill, Streamer, SCAN1000 or Excel software. The serial Microlinks (those that communicate over RS232 or RS485) can be OPC-enabled. With the addition of their OPC-server software you can use them with any OPC client software such as Hexatec's Saturn SCADA software and National Instruments' LabVIEW. Another option is to program the Microlink yourself: ask for our programming manuals and example programs.

Use with the 3070 High Speed Scanning Module

The analogue input facilities of the Microlink can be used in 2 modes. Systems without a 3070 module, or with the 3070 disabled, take single samples on demand. The computer addresses one of the analogue input modules, which then connects its signal to the analogue-to-digital converter. A single conversion is performed and the digitised data passed to the computer. In this mode, sampling is controlled directly by software. When a Microlink 3070 module is used, the channels which are to be digitised are selected before data collection begins. The 3070 is then programmed to multiplex the selected inputs and take samples at precise time intervals.

More Information

For more details on about monitoring analogue signals:


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