31-03-2013, 06:34 PM
Y'know Lawrence, I think you right about that!
I say that because the scale of this ex-TF144G meter - which is a moving-coil movement - on test, is non-linear. The scale is marked in linear calibrations, but when an adjustable and separately-monitored current is passed through the meter, the readings are not linear. From your attachment, I understand that a thermo-couple is non-linear as regards its voltage O/P versus temperature. So I can only assume that the scale of this meter takes that non-linearity into account and thus produces an (approximate) linear scale. Having said that, of course, the accuracy of the linearity is a bit irrelevant anyway, since the primary purpose of this meter is to 'set' the carrier wave level: the 'set carrier' mark at the centre of the linear meter scale.
All of which presents me with an interesting little problem. If I want to use this meter in an application other than its intended use (and that is 99% guaranteed), do I attempt to design a substitute linearisation cct. or do I simply re-scale the meter and accept the consequent non-linear calibration? Obviously, the latter is the easiest, but the resulting scale won't look anything like as professional.
Any suggestions?
Al.
I say that because the scale of this ex-TF144G meter - which is a moving-coil movement - on test, is non-linear. The scale is marked in linear calibrations, but when an adjustable and separately-monitored current is passed through the meter, the readings are not linear. From your attachment, I understand that a thermo-couple is non-linear as regards its voltage O/P versus temperature. So I can only assume that the scale of this meter takes that non-linearity into account and thus produces an (approximate) linear scale. Having said that, of course, the accuracy of the linearity is a bit irrelevant anyway, since the primary purpose of this meter is to 'set' the carrier wave level: the 'set carrier' mark at the centre of the linear meter scale.
All of which presents me with an interesting little problem. If I want to use this meter in an application other than its intended use (and that is 99% guaranteed), do I attempt to design a substitute linearisation cct. or do I simply re-scale the meter and accept the consequent non-linear calibration? Obviously, the latter is the easiest, but the resulting scale won't look anything like as professional.
Any suggestions?
Al.
