D.C. PICOVOLTMETER MODEL P13a
The EM DC Picovoltmeter Model P13a is an ultra sensitive instrument which can amplify and measure DC potential down to about 20 picovolts (2 X 10e-11 volts).
It is ideal for use as a null detector for low impedance bridge balancing.
The noise performance is such that, using a source impedance of 0.25 ohm or higher, the detection level will be limited by the Johnson noise of the source. The equivalent noise resistance of the P13a is only 250 milli-ohms. To make full use of the noise performance, it is desirable to use it with low source impedance. While the P13a can be operated with source impedance of 10K ohm or more, its characteristic will be overwhelmed by the source noise if the source impedance is too high. Great care must be taken with the input leads and connections, to keep their resistance below the equivalent noise resistance of the instrument if possible.
In order to realise ultra low detection levels, the drift characteristics with temperature and time have to be maintained to levels which have been hitherto unattainable.
The design of the P13a ensures that, even in normal laboratory environments, the lower
ranges are easy to use.
The excellent stability of this instrument means that it is deal for long term drift measurements, and may be coupled to a recorder and left unattended for long periods.
A six position filter gives the user control over the response time and reduction of noise from the circuit being measured.
A calibrated offset voltage control is provided with an eleven position multiplier switch, giving a maximum offset of plus and minus 100 micro-volts. This can be used to measure small changes in comparatively large signals. The level of input which can be offset on any range will be limited only by the resolution of the calibrated potentiometer, i.e. about 0.01%.
The pure copper input terminal arrangement, with shield, allows easy connection to the circuit to be measured.
A second input is provided, in conjunction with a switch on the front panel, which decreases the sensitivity of the basic ranges by one million times.
There are two outputs at the rear of the instrument, one direct and the other isolated. The direct output is used where maximum linearity is required although the isolator also has good linearity.
The instrument is battery operated from internal chargeable batteries and so has the advantage of complete isolation. There are two modes of battery charging.
The instrument may be connected to the mains supply and use the specially designed multiple screened toroidal mains transformer, or a separate connector is provided so that an external current generator may be used to maintain the battery charge. The latter mode may be useful when long term resolution of small signals is required.
The P13a is engineered to a very high standard and comes complete with a terminal shield, which simply plugs onto the two outer front terminals.
SPECIFICATION D. C. PICOVOLTMETER MODEL P13a
Series Mode Rejection
Contact EM Electronics
|Queen's Award for Technological Achievement 1990. The DTI SMART Award.|