The Microlink 752 unit plugs into the computer's USB port and provides differential inputs to monitor resistance, RTDs, Pt100 probes and voltage signals. The units also offer digital input and output, counting, and voltage or current output control. You can connect 8 USB units to 1 PC.
Resistance measurements are made by passing a constant, known, current through the unknown resistance, and monitoring the voltage drop across the resistance. The 752 unit has a constant current source of 1 milliamp.
When the resistance to be measured is small, the resistance in the leads to the sensors can significantly affect accuracy. However, different wiring configurations allow the lead resistance to be measured and compensated for. The Microlink 752 gives excellent results for all configurations, including 2 wire, 3 wire, 4 wire and 4 wire compensated. The most accurate results are obtained using a 4 wire arrangement. More connections are required for these arrangements than for straightforward voltage measurement. This means that you can monitor 16 voltages or 8 resistances, or a combination of the two such as 8 voltages and 4 resistances.
RTDs rely on the principle that the resistance of a metal increases with temperature. For extreme precision, the resistance element is made of platinum and the RTD known as a platinum resistance thermometer (PRT). When specified to have a resistance of 100 Ohm at 0 oC, RTDs are referred to as Pt100 probes. Windmill automatically converts the resistance measurement to a temperature in your choice of engineering units.
The resolution of measurements is set through Windmill software. You can choose from 12 to 18 bits: for fast speeds or high resolution. There are 4 input ranges on offer, and Windmill can automatically select the range most closely encompassing the signals.
The 752 provides 24 digital I/O lines, arranged in three ports, or groups, of 8. Use Windmill to choose whether each port is an input or an output. You can read or set the state of each line individually. Alternatively, you can switch several channels at the same time.
The Microlink 752 has eight 16-bit totalling counters. Each counter starts at zero and counts pulses to a maximum of 65535. You can reset a counter at any time from Windmill software. You can use the counters in two modes: accumulating count and resetting count. In accumulating count the counter keeps counting until you reset it. In resetting count the counter shows the number of pulses since the last reading.
You can set a scale and offset factor to the count from software. For example if the pulses came from a flow meter which produced one pulse for every 50 millilitres, a scale factor of 0.05 would give a reading in litres.
The counters are found on 8 of the digital input and output lines. You can use any of these you don't need for counting as normal digital inputs: the counts are always maintained even if you don't plan to use them.
By adding a Microlink 593 unit, which provides cold junction measurement, you can also monitor thermocouples. For strain gauges you need a Microlink 594 connection box and excitation supply.
The slim Microlink 752 provides pin connections for your signals. However, if you prefer to use screw-terminals these are provided by our Microlink 590 unit. This also allows many extra facilities, such as:
The latest version of Windmill is supplied with the Microlink 752. This modular suite offers data logging, charting, alarm indication, output control and DDE links to other applications like Excel. You can also add process mimic generators, sequence control and many other modules. Should you wish to program the 752 yourself, you can use the IML Tools to do so.
The Microlink 752 package starts at 795 pounds. You can order over the internet through Windmill Software's Data Acquisition and Control Catalogue. Alternatively ask us for a quotation for the Microlink 752. Please give as many details as possible about your application: including the number and type of transducers to be monitored. You can also use the quote form simply to ask our advice about your project.
USB, or universal serial bus, ports are found on most new computers. They are gradually replacing the serial and parallel interfaces we're used to. As well as using the USB port for the Microlink 752, you can connect peripherals like printers, scanners, digital cameras and telephones. You can unplug the Microlink then plug it back as you wish, with no need to restart Windows inbetween.
The USB cables shouldn't be longer than 5 metres. However, using USB hubs between cables you can reach 30 metres away from the PC. If you need longer distances, network PCs together over Ethernet (or consider our RS485 and Ethernet Microlinks - contact us if you would like our advice).
For more details on the universal serial bus see our USB Technical Notes page.
Dimensions (mm) 180 x 120 x 40 Maximum length of cable 5 m Maximum distance from PC can be increased by use of USB hubs ANALOGUE INPUTS Current source 1 milliampere Maximum resistance inputs 8 Maximum voltage inputs 16 Maximum safe input voltage: Power supply on ±48 V Power supply off ±33 V Transient ±300 V Analogue to Digital Converter: Maximum linearity error ±0.02% Resolution Integration Time Samples/Second 12 bits 2.5 msec 80 13 bits 5 msec 64 14 bits 10 msec 48 15 bits 20 msec 32 16 bits 40 msec 16 18 bits 160 msec 6 ANALOGUE OUTPUTS Max # analogue outputs 2 Voltage output 0-10.240 V Max # voltage outputs 2 Current output 0-20.480 mA Max # current outputs 2 Resolution 12 bits DIGITAL INPUTS/OUTPUTS Maximum number inputs 24 Maximum number outputs 24 (selected through Windmill in ports of 8 lines) Power-up state all inputs Compatibility TTL and 5 V CMOS, can be made contact closure compatible Range 0 to 5 V Output capability 15 LSTLL loads Maximum I/O speed 160 channels per second COUNTERS Maximum number counters 8 Resolution 16 bits Compatibility TTL, 5 V CMOS, can be made contact closure compatible Input voltage range 0 to 5 V Maximum count speed 160 counts per second