Can a regular multimeter measure voltages in 400hz range?

Thread Starter

Rahulk70

Joined Dec 16, 2016
533
Hi,

I’m building a test bench for some aircraft instruments and I was testing a Bendix 1964771-3 inverter(24 VDC) brought from eBay. The inverter should have outputs of 129VAC @ 370Hz @ 12VAC/18VAC @ 1110 Hz. The inverter was marked as untested but removed working from an aircraft I was told. So, powered up the inverter and checked the outputs with a Unit-T UT33C multimeter. But I was not getting any output. I suspect maybe only the expensive ones like fluke, omega etc can measure such high frequency voltages. Could this be the case? Just as a precaution I tried using a neon voltage tester and it immediately lit orange light.

Thanks
 
Last edited:

Reloadron

Joined Jan 15, 2015
6,836
This should be your meter. The specifications on page 32 spell out a frequency range of 40 to 400 Hz for AC voltage measurements. This assumes you are looking in the right places and the UUT (Unit Under Test) is properly powered up on your test bench.
The same is true of the Turn and Slip indicator. If the unit is properly powered up it should indicate correctly.

Ron
 

Thread Starter

Rahulk70

Joined Dec 16, 2016
533
This should be your meter. The specifications on page 32 spell out a frequency range of 40 to 400 Hz for AC voltage measurements. This assumes you are looking in the right places and the UUT (Unit Under Test) is properly powered up on your test bench.
The same is true of the Turn and Slip indicator. If the unit is properly powered up it should indicate correctly.

Ron
Hello Ron,

The turn and slip indicator runs of 12-32VDC. I powered it directly from pins but only the red flag was disappearing. So no power to the gyro motor. So, turns out the above mentioned IC is dead. But cant find any datasheet on it.
 

crutschow

Joined Mar 14, 2008
30,463
So, powered up the inverter and checked the outputs with a Unit-T UT33C multimeter. But I was not getting any output.
The meter should read some output at 400Hz, even if it's not accurate so, no output indicates a measurement problem.

Does the meter measure the 60 Hz main's voltage ok?
 

Reloadron

Joined Jan 15, 2015
6,836
Back to the beginning your meter according to the specifications for that make and model should read AC between 40 and 400 Hz.
The inverter should have outputs of 129VAC @ 370Hz @ 12VAC/18VAC @ 1110 Hz.
The 129 VAC @ 370 Hz should not be a problem but the 12 VAC and 18 VAC @ 1110 Hz. is well above the meter's AC frequency limits. Not sure why you have two @ symbols in there?

The inverter is designed for a 24 VDC input but I haven't a clue as to the input power current requirements? I can only assume you have sufficient current @ 24 VDC? The outputs are either there or they aren't. The fact that someone days the unit was untested but removed from aircraft working really isn't much help. Functioning units are seldom removed from aircraft unless the aircraft is being scrapped going to an aircraft bone yard. I am also unsure about the 1.110 KHz frequency as it just sounds a bit unusual for an aircraft.

Ron
 

rsjsouza

Joined Apr 21, 2014
361
Nowadays it is very uncommon for a portable DMM to have a bandwidth lower than 400Hz - this is mostly due to the cost reduction in electronics that can manufacture cheap faster ADCs.
 

MrSalts

Joined Apr 2, 2020
2,111
Make sure your meter is set to AC voltage. Turn to the 5-o'clock position (approximately). 200v AC range should work fine.
 

Alec_t

Joined Sep 17, 2013
13,077
If your meter AC ranges can't cope with the frequency you could rectify the inverter output to get a rough estimate of output voltage.
 

panic mode

Joined Oct 10, 2011
2,222
it could be that your multimeter is not working correctly. do you have a second one?
also an oscilloscope is a very useful piece of equipment for any bench... it can show things that multimeters cannot.
 

Thread Starter

Rahulk70

Joined Dec 16, 2016
533
it could be that your multimeter is not working correctly. do you have a second one?
also an oscilloscope is a very useful piece of equipment for any bench... it can show things that multimeters cannot.
I used a better multimeter loaned from my workplace (Omega HHM9007R) this time and checked the voltage. Now I'm able to see the readings properly and it shows with one pair 113VAC & second pair of output 129VAC. The frequency is at about 389Hz.
 

Thread Starter

Rahulk70

Joined Dec 16, 2016
533
Back to the beginning your meter according to the specifications for that make and model should read AC between 40 and 400 Hz.

The 129 VAC @ 370 Hz should not be a problem but the 12 VAC and 18 VAC @ 1110 Hz. is well above the meter's AC frequency limits. Not sure why you have two @ symbols in there?

The inverter is designed for a 24 VDC input but I haven't a clue as to the input power current requirements? I can only assume you have sufficient current @ 24 VDC? The outputs are either there or they aren't. The fact that someone days the unit was untested but removed from aircraft working really isn't much help. Functioning units are seldom removed from aircraft unless the aircraft is being scrapped going to an aircraft bone yard. I am also unsure about the 1.110 KHz frequency as it just sounds a bit unusual for an aircraft.

Ron
I found those values from here:

https://www.prc68.com/I/Gyroscopes.html#Bendix_Static_Inverter

Strangely though I found it to be little different and all the frequencies I measured were only about 369Hz.
 

Reloadron

Joined Jan 15, 2015
6,836
I used a better multimeter loaned from my workplace (Omega HHM9007R) this time and checked the voltage. Now I'm able to see the readings properly and it shows with one pair 113VAC & second pair of output 129VAC. The frequency is at about 389Hz.
Well now it makes more sense. Your original meter should have worked according to the data sheet I recall linking to but obviously not. Nice find on the inverter. Peculiar outputs but I guess it was designed for a purpose and it apparently served that purpose.

Ron
 
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