Waveform input
Waveform input channels are buffered through amplifiers. If the programmable-gain option is fitted, the gains are individually software-settable to unity, x2, x5 or x10. Channels are then steered into the ADC (Analogue to Digital Converter) via multiplexers. The input sample-and-hold is part of the ADC chip. The ADC converts an input voltage to a 16-bit digital value in approximately 0.5microSec and changing channels takes another 0.5, so the maximum single channel speed is 2MHz, which reduces to 1MHz for multi-channel capture. Sampling is inherently sequential; two channels cannot be sampled simultaneously.
Waveform channels
There are 16 waveform input channels on a standard Power1401. Eight channels are available through front-panel BNC connectors, labelled ADC Inputs, and eight through the rear-panel Analogue Expansion D-socket. The normal working input range of these channels is ±5V, but can be altered to ±10V by cutting and soldering a pair of links.
Trigger
There is a front-panel input labelled Trigger. This can be set by software to be the external signal to start the ADC converting. The ADC external convert input is also permanently wired through pin 6 of the rear panel Events D-socket. Conversions are usually initiated by a high-to-low transition. External convert signals are used when the conversion time is determined by an external event, e.g. when synchronising conversions to the phases of a rotating machine. When operating in internally-triggered mode the ADC typically samples at a fixed rate set by one of the clocks.
ADC LEDs
The front-panel waveform input channels each have an associated yellow LED. They are controlled purely by software command and turn on when the channel is in use.
Trigger LED
The trigger-input LED flashes on detection of an active-edge transition at the Trigger input. The LED can be set by software to be either on or off during its quiescent state.
Technical details: Analogue input
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 ±15V. If you do overdrive the inputs, it is possible to damage the input buffer amplifiers. These chips are in sockets for easy replacement.
The system accuracy and noise are 0.05% of full scale, ±1.5 bits.
Trigger input
The front-panel Trigger input has in-line over-voltage protection and can accept signals in a ±40V range (absolute maximum). This input is held internally to +5V by a 100 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 50microA. Pulses driving the trigger input should be 1microSec or longer.
The rear-panel ADC external-convert input responds to TTL and switch closure signals, and 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 switches.
The ADC
The input voltage is resolved into 65536 levels (16-bit precision); each step is approximately 150microV. Out-of-range voltages can cause incorrect output values and should be avoided. There is an option of programmable gain, x1, x2, x5, x10 on the 8 waveform inputs.
Waveform output
There are 4 waveform output channels on the Power1401. Two are available through BNC connectors on the front panel, labelled DAC Outputs (Digital to Analogue Converters), and two through the rear-panel Analogue Expansion D-socket.
The DAC waveform outputs produce voltages in the range ±5V, in steps of approximately 150microV. If the programmable gain option has been fitted, the output gain can be switched by software between unity and x2. Alternatively, the range can be altered semi-permanently to ±10V, and 300microV resolution, by cutting a PCB track next to each DAC.
The DACs can be set by program to update in response to an external signal, either the rear panel Event Clock F input or the front panel Trigger input, to synchronise the update rate to external equipment. When multiple channels of waveform are output, the Power1401 can be programmed to update several DACs simultaneously. The maximum update rate is 400kHz.
DAC LEDs
The front-panel waveform output channels each have an associated yellow LED. The LED turns on when the channel is in use.
Technical details
The waveform outputs are designed for driving loads of 600 Ohms impedance or higher, and are short-circuit proof. For full accuracy, the load should not be less than 5 kOhm. The output amplifiers are fitted in sockets for easy replacement.
