Pokit Calibration Guide

All Pokit Devices are factory calibrated during production and shouldn’t require calibration in most instances. However, all measurement devices can drift over time and need to be recalibrated eventually to ensure accuracy is maintained. Also, it may be required to meet compliance if you are using your Pokit Device in a professional setting. It is best to have your Pokit Device calibrated manually. Read on below to find out how!

The following Guide outlines the methodology and best practices for calibrating your Pokit Device.

Currently, only Pokit Pro can be calibrated manually, but Pokit Meter will have calibration enabled in a future update.

There are a few things you need before you get started:

1. Your Pokit Device.
2. A Calibrated multimeter with an in-date, traceable calibration. Ideally, the calibrated multimeter has at least double the precision of the Pokit Device in the ranges being tested.
3. Calibration standards of known or stable values. A common type of calibration standard is a precision resistor or a calibrated voltage source.
4. A temperature and humidity-controlled environment set to 22 ˚C - 28˚C & 50% – 70% RH.
5. Any required safety equipment.
6. An Isolation Transformer and the Banana Connector accessory are recommended for high voltages on Pokit Pro.

WARNING:

Improper calibration can lead to poor measurement quality, which has the potential to cause harm to people and equipment.

Calibrating a multimeter requires a certain level of technical knowledge and expertise, so it is recommended that you seek professional assistance or contact a calibration lab if you are not familiar with the process.

Calibration Standards

There are two types of calibration standards that can be used for calibration:

1. Precision Standards:
   A Precision Standard is a calibration standard that can be relied upon inherently to produce a precisely known current/voltage/resistance etc. under the correct temperature and humidity conditions. An example of a precision standard would be a Fluke 5502A.
2. Stable Standards:
   A Stable Standard is a calibration source of current/voltage/resistance etc. that may not be precisely known but does not vary significantly over the duration of testing that can be used in conjunction with a calibrated multimeter for calibration.

Ideally, Precision Standards would be used for calibration. However, most people will find it challenging to get their hands on and use a Precision Standard. So, a Stable Standard may be used instead, so long as it can be shown to be stable.

Some of Stable Standards are below:

For a Stable Standard to be considered stable, its noise level and variance must be constant (capacitors and resistors can be considered inherently stable so long as the ambient temperature is stable).

Noise Level:

The noise level of the source can be determined by looking at the oscilloscope trace and comparing the signal to an ideal signal. For a DC Signal, the noise can be calculated to be AVG subtracted from RMS.

Example 1: Noise level test in oscilloscope mode

Variance:

The Variance of a signal can be determined by logging the signal over a 10-minute period and looking at the peak-to-peak difference in the log.

Example 2: Variance of signal test in logger mode

Calibrating using the App

Below is an example of calibrating the 0-250mV range on a Pokit Pro:

1. Set the Pokit Pro to Multimeter DC Voltage. If you are unsure how to do this, refer to the Pokit Pro manual.
2. Verify the accuracy of the voltage range: To verify the voltage range, connect the multimeter to the calibration standard set in the Voltage range being tested (0-250mV in this case). The reading on the multimeter should match the value of the calibration standard.
3. If the reading is incorrect, repeat Step 2 for 25% and 75% of the range and put the calibration standard and the Pokit Pro’s measurements in the appropriate column in the calibration spreadsheet for Pokit Pro (download from the bottom of this help article).
4. Navigate to the Calibration screen by tapping the cog on the Devices screen and then tapping on the CALIBRATE button.

Example 3: Devices Screen Navigation

Example 4 Settings Screen Navigation

5. Get the existing calibration Gain and Offset for the appropriate range (in this case, 0-250mV) and enter it into the appropriate column in the calibration spreadsheet for Pokit Pro (download at the bottom of this help article).
6. The calibration spreadsheet will calculate an appropriate Gain and Offset that can be entered into the calibration screen on the App.

Example 5 Calibration Screen

• • Alternatively, for bulk calibration you can export the calibration data as a CSV, edit it and import the data back into the App.

7. You can confirm the calibration of the range by repeating Step 2.
8. Repeat the process for other ranges and modes.

Pokit Pro Calibration Ranges

AC Voltage and AC Current use positive calibration values.

External Temp relies on resistance measurement accuracy in the 0 to 500k ranges, so resistance must be calibrated to get a correct reading.

Further Advice

• If a benchtop power supply is used for DC Low current calibration on Pokit Pro (0-300mA), a resistor should be placed in series with the circuit to avoid the fuse blowing. The Current Regulation on most benchtop power supplies is set to start at max output current (typically ~3A) and then regulate down to the selected current. Putting a resistor in series allows the user to limit the current by selecting the max voltage and relying on Ohms Law to restrict the max current. For example, a power supply set to 10V,100mA with a 27Ω resistor will restrict the current to an initial current of 370mA, and then the PSU will regulate down to 100mA.
• For very low currents (<10mA), a desktop Power Supply may be used in conjunction with a resistor to generate the low current where Voltage is used to control the current through the resistor using Ohms Law.
• Use Probe Clips for connecting to resistors and capacitors. If you handle the leads of resistors and capacitors while measuring them, your body can act as a parallel resistor and interfere with the measurement.

Example 6 The correct method of connecting a resistor to a Pokit Pro for calibration.

• When handing discreet resistors and capacitors, you can inadvertently heat them up due to your body temperature. To avoid this affecting your calibration results, you should wait 10 minutes after handling a capacitor or resistor before taking a measurement.
• If a calibrated multimeter and a stable standard are used to calibrate a Pokit Device, then the quality of the calibration is dependent on the quality of the calibrated multimeter’s calibration. Ensure the calibrated multimeter is calibrated appropriately and the calibration is to date.
• If your Pokit Pro is measuring 0-50V on a 110-240V Mains supply, then the issue is likely not calibration. Most likely, the 500mA fuse is blown (some small voltage may still be read due to capacitive coupling). If replacing the 500mA fuse doesn’t help, then please submit a support request and our technical support team will be able to assist you.
• Employ appropriate safety precautions when calibrating using Mains Voltages such as appropriate PPE, an isolation transformer is also advised, and the banana connectors accessory should be used with Pokit Pro in conjunction with appropriately rated shrouded banana cables. If you are unsure or unfamiliar with working with Mains Voltages, then you are strongly advised to contact a calibration lab rather than doing it yourself.