Waveform input channels

There are 4 waveform input channels on an unexpanded Micro1401-3. These channels are available through front panel BNC connectors, labelled ADC Inputs (Analogue to Digital Converter). The normal working input range of these channels is ±5 Volts or ±10 Volts, software selectable.

Micro1401 Waveform input channels

There is also a BNC input labelled Trigger. When the program requires it, this is set to be the ADC external convert input. The ADC external convert input is always available on pin 6 of the rear panel Events Cannon 15 pole socket. The input may be used to cause waveform channels to be sampled at times determined by external signal pulses, for example to lock conversion times to the positions of a rotating machine.

All of these front panel inputs, and the front panel outputs, have an associated LED indicator light that comes on, or flashes (as appropriate) when that signal connector is active.

More input channels may be added with top boxes

Technical details

The input impedance of the waveform channels is typically 1 MOhm. The waveform inputs expect to be driven from a low-impedance source (100 Ohms or less); the output of most amplifiers is suitable. The maximum non-destructive input voltage range is ±12 Volts. If you do overdrive the inputs, it is possible to damage the input buffer amplifiers. These chips are in sockets for easy replacement.

The Micro1401-3 resolves the input voltage into 65,536 levels (16 bit precision); each level is approximately 150 µV, or 300 µV on the ±10V range.

The ADC external convert input responds to TTL and switch closure signals and has overvoltage protection. Via the front panel Trigger input, it can accept signals in a 40V range (absolute maximum). This input is held internally to +5V by a 47 kOhm resistor and has input hysteresis: the low-going threshold voltage is set at 0.95V and the high-going threshold at 1.2V. To pull this input low, the driving device must be able to sink 100 µA. Pulses driving the trigger input should be 1µs or longer.

The rear panel input is held internally at +5V via a 10 kOhm resistor. Input pulses should not be narrower than 1µs and must fall below 0.8V for guaranteed recognition. This input is protected by a 100 Ohm series resistor and diode clamps to +5V and ground; the safe range is 0 to +5V. Conversion is normally initiated on the high-to-low edge. Use of the other edge can be selected by an internal switch.

Waveform output channels

There are 2 waveform output channels on the Micro1401-3 available through BNC connectors on the front panel, labelled DAC Outputs (Digital to Analogue Converters).

Micro1401 Waveform output channels

The DAC waveform outputs produce voltages in the range ±5 Volts, in steps of approximately 150 µV, or 300 µV on the ±10V range.

When multiple channels of waveform are output, the DACs can be programmed so that they both change simultaneously. The maximum update rate is in excess of 400kHz; this is reduced when performing other activities, as is usual in high level software.

The DACs can also be set by program to update in response to an external convert signal, on pin 2 of the rear panel Events connector, or the front panel Trigger input, synchronising the output rate to external equipment.

Technical details

The waveform outputs are designed for driving loads of 600 Ohms or higher impedance and are short-circuit proof. For full accuracy, the load should not be less than 5 kOhms. The output amplifiers are fitted in sockets for easy replacement.

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