Once the frequency has been set, the lock key engages a measure-and-correct circuit which compensates for the small thermal and mechanical drifts that inevitably occur
The TG550 from TTi (Thurlby Thandar Instruments) is a 5MHz function generator which incorporates a digital frequency locking system that gives it a level of frequency stability that, says TTi, cannot be matched by conventional analogue function generators.
The frequency is compared to a crystal-controlled reference, and is maintained to an accuracy of better than one digit on the display.
The TG550 provides simultaneous digital display of frequency and level.
A large LCD display shows frequency in the left-hand half and output level in the right-hand half.
Auto-ranging reciprocal frequency measurement gives four-digit resolution with rapid update right down to 2Hz. Accuracy is within +/-1 digit (+/-0.02% at full scale).
To maintain a fast update below 2Hz, the measurement mode is changed, resulting in three-digit resolution.
When compared to the normal fixed gate-time meters used in other products, the TG550 provides both higher accuracy and faster display update across the whole frequency range.
The output level display can be selected to show any of three values: peak-to-peak amplitude, RMS amplitude or DC offset.
The decimal point and units are changed automatically, resulting in a display of the true amplitude regardless of the attenuator setting.
The TG550 generates sine, square, triangle, pulse and ramp waveforms from 0.005Hz up to 5MHz.
A built-in sweep generator provides linear or logarithmic sweeps, with periods ranging from 20ms to 20 seconds.
AM capability is also incorporated, with a choice of internal or external modulation from 0 to 100%.
The TG550 has an external counter mode which utilises the full width of the display to provide up to seven digits of resolution.
The frequency range is from 5Hz up to 20MHz, and the input sensitivity is better than 50mV RMS.
Accuracy is typically better than ten parts per million, and an external adjustment point allows re-calibration when high accuracy is essential.
A measurement period of 0.5 or 5 seconds can be selected.
Reciprocal counting ensures high resolution regardless of input frequency.
Thus, for example, mains frequency can be measured to a resolution of 0.001Hz.
The TG550 costs £349 (plus VAT).
