|Hytec Electronics Ltd.|
VME VOLTAGE TO FREQUENCY CONVERTER TYPE VFC 2504
This unit is an 8 channel voltage–to–frequency converter housed in a 6U high single–width VME module. No signal connections are made to the VME bus, only power is picked up. Inputs are 0 to 10 volts differential with 0 to 1 volt and 0 to 100 millivolt ranges also available using jumpers; outputs are available in both TTL and Fast NIM form.
Isolated single pole LEMO (RA 00250) connecters are used to input eight unipolar analogue signals isolated from the VME bus ground. Optionally, two–pole LEMO connectors (RA0304) may be used, allowing much higher common mode voltages to be accomodated. The input stage is a differential amplifier operating from an isolated power supply. The input stages do not have their own power supplies, they have one between two, thus pairs of inputs need to be reasonably closely tied in terms of potential from ground ( within 3 volts or so) but between pairs the isolation of the power supplies means that there may be a potential difference of up to 2000 volts, except that this voltage will appear on the metal case of the 00250 connector, which is dangerous to say the least. In the single pole LEMO version, therefore, +/– 48 volts is the recommended maximum swing either side of the ground. With the double–pole connectors, the limitation will be the cabling and the PCB tracks, perhaps 500 volts is a more reasonable figure.
The input amplifiers have a jumper to connect one side (normally the screen side) of the input to isolated common, to give a single–ended input form. Two further jumpers select 0 to 1 volt input range and 0 to 100 millivolt: neither jumper fitted gives 0 to 10 volts. Performance figures are specified for 10 volt and1 volt ranges. The offset of the input amplifier is adjusted to give the same value in 10 volt and 1 volt modes. Full scale referred to the output of the voltage–to –frequency converter is calibrated in the 10 volt range: there is a maximum gain error of +/–0.05% in the 1 volt range (+/–0.005% typical) and +/–0.1% max. in the 100 millivolt range (+/–0.01% typical) which cannot be trimmed, although recalibration to either 1 volt or 100 millivolt range is quite straightforward.
Voltage to Frequency Converters
The output of each input amplifier is fed to a synchronous V–to–F converter whose output is 0 to 1 MHz full scale. Offset adjustment is used to set zero scale and full scale is adjusted to give 1 MHz at 10 volts or 1 volt input depending on the input range. Each pair of V–to–F converters has its own quartz crystal oscillator which governs the full scale output frequncy.
The outputs of the V–to–F converters are fed to logic opto–isolators which then produce TTLfrequency signals referred to VME bus grounds.
Eight TTL driver output stages feed buffered frequency signals to a 16–way header on the front panel (signals on even pins, grounds on odd pins – compatible with the EC738 scaler – Hytec catalog number 2382).
Eight TTL–to–NIM converters produce fast –1 volt into 50 ohm NIM signals for output via single pole LEMO sockets (RA 00250) on the front panel.
(After allowing a warm–up period of ten minutes.)
Fixed temperature performance:
In the 0 to 10 volt range, the accuracy of this unit is guaranteed to be better than +/–0.03% over a 20 degrees C temperature band ( 10 degrees either side of set up temperature ) and will typically be better than +/–0.02%.
|Hytec Electronics Ltd
Post : 5 Cradock Road, Reading, Berkshire, RG2 0JT, England.
Phone : +44 (0)118 9757770
Fax : +44 (0)118 9757566
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